Changes to @earth_day and @earth_night grids from GMT 6.4 to 6.5?

Just checking something that I noticed at https://github.com/GenericMappingTools/pygmt/pull/2963#discussion_r1444072938. Are the Blue Marble `@earth_day_01d_p` and Black Marble `@earth_night_01d_p` datasets only downloadable with GMT 6.5.0 (and not GMT 6.4.0 or older) now?

E.g. doing `gmt which @earth_day_01d_p -Vd` with GMT 6.4.0 gives:

```
gmt [DEBUG]: GMT_Create_Session: Terminal width = 190
gmt [DEBUG]: Obtained the ppid from parent: 3763
gmt [DEBUG]: Enter: gmtinit_new_GMT_ctrl
gmt [DEBUG]: GMT->session.SHAREDIR = ~/mambaforge/envs/pygmt/share/gmt
gmt [DEBUG]: GMT->session.HOMEDIR = ~
gmt [DEBUG]: GMT->session.USERDIR = ~/.gmt [created]
gmt [DEBUG]: GMT->session.CACHEDIR = ~/.gmt/cache [created]
gmt [DEBUG]: GMT: 0. Will try to find subdir=postscriptlight stem = PSL_custom_fonts suffix=.txt
gmt [DEBUG]: GMT: 1. gmt_getsharepath trying current dir
gmt [DEBUG]: GMT: 2. gmt_getsharepath trying USERDIR ~/.gmt
gmt [DEBUG]: GMT: 3. gmt_getsharepath trying USERDIR subdir ~/.gmt/postscriptlight
gmt [DEBUG]: GMT: 4. gmt_getsharepath trying SHAREDIR subdir ~/mambaforge/envs/pygmt/share/gmt/postscriptlight
gmt [DEBUG]: GMT: 5. gmt_getsharepath trying SHAREDIR ~/mambaforge/envs/pygmt/share/gmt
gmt [DEBUG]: GMT: 6. gmt_getsharepath failed
gmt [DEBUG]: Map distance calculation will be Cartesian
gmt [DEBUG]: Exit: gmtinit_new_GMT_ctrl
gmt [DEBUG]: Enter: New_PSL_Ctrl
gmt [DEBUG]: Exit: New_PSL_Ctrl
gmt [DEBUG]: Enter: gmt_manage_workflow
gmt [DEBUG]: Exit : gmt_manage_workflow
gmt [DEBUG]: Enter: PSL_beginsession
gmt [DEBUG]: Exit : PSL_beginsession
gmt [DEBUG]: Enter: PSL_setdefaults
gmt [DEBUG]: Exit : PSL_setdefaults
gmt [DEBUG]: Enter: gmtlib_io_init
gmt [DEBUG]: Exit : gmtlib_io_init
gmt [DEBUG]: Enter: gmt_hash_init
gmt [DEBUG]: Exit: gmt_hash_init
gmt [DEBUG]: Enter: gmt_hash_init
gmt [DEBUG]: Exit: gmt_hash_init
gmt [DEBUG]: Enter: gmt_reload_settings
gmt [DEBUG]: The PROJ_GEODESIC set to Vincenty
gmt [DEBUG]: Look for file ~/gmt.conf
gmt [DEBUG]: Look for file ~/.gmt/gmt.conf
gmt [DEBUG]: Look for file ~/.gmt/server/gmt.conf
gmt [DEBUG]: Look for file ~/.gmt/cache/gmt.conf
gmt [DEBUG]: Could not find file gmt.conf
gmt [DEBUG]: Exit: gmt_reload_settings
gmt [DEBUG]: Enter: gmtlib_plot_C_format
gmt [DEBUG]: Exit: gmtlib_plot_C_format
gmt [DEBUG]: Enter: gmtinit_get_history
gmt [DEBUG]: Initialize FFTW with 16 threads.
gmt [DEBUG]: GMT_Create_Session initialized GMT structure
gmt [DEBUG]: Loading core GMT shared library: libgmt.so
gmt [DEBUG]: Shared Library # 0 (core). Path = libgmt.so
gmt [DEBUG]: Loading GMT plugins from: ~/mambaforge/envs/pygmt/lib/gmt/plugins
gmt [DEBUG]: Shared Library # 1 (supplements). Path = ~/mambaforge/envs/pygmt/lib/gmt/plugins/supplements.so
gmt [DEBUG]: Local file ~/.gmt/server/gmt_data_server.txt found
gmt [DEBUG]: File ~/.gmt/server/gmt_data_server.txt less than 24 hours old, refresh is premature.
gmt [DEBUG]: Load contents from ~/.gmt/server/gmt_data_server.txt
gmt [DEBUG]: Local file ~/.gmt/server/gmt_hash_server.txt found
gmt [DEBUG]: File ~/.gmt/server/gmt_hash_server.txt less than 24 hours old, refresh is premature.
gmt [WARNING]: Remote dataset given to a data processing module but no registration was specified - default to gridline registration (if available)
gmt [DEBUG]: Input remote grid modified to have registration: @earth_day_01d_p
gmt [DEBUG]: Map distance calculation will be using great circle approximation with authalic auxiliary latitudes and authalic (R_2) radius = 6371007.1809 m, in meter.
gmt [DEBUG]: Revised options: @earth_day_01d_p -Vd
gmtwhich [DEBUG]: gmtapi_init_export: Passed family = Data Table and geometry = Non-Geographical
gmtwhich [DEBUG]: Object ID 0 : Registered Data Table Stream 7fd32ddf2780 as an Output resource with geometry Non-Geographical [n_objects = 1]
gmtwhich [DEBUG]: gmtapi_init_export: Added stdout to registered destinations
gmtwhich [DEBUG]: GMT_Init_IO: Returned first Output object ID = 0
gmtwhich [DEBUG]: GMT_Begin_IO: Initialize record-by-record access for Output
gmtwhich [DEBUG]: gmtapi_next_io_source: Selected object 0
gmtwhich [INFORMATION]: Writing Data Table to Standard Output stream
gmtwhich [DEBUG]: GMT_Begin_IO: Output resource access is now enabled [record-by-record]
gmtwhich [DEBUG]: Look for file earth_day_01d_p.tif in ~/.gmt
gmtwhich [DEBUG]: Look for file earth_day_01d_p.tif in ~/.gmt/cache
gmtwhich [DEBUG]: Look for file earth_day_01d_p.tif in ~/.gmt/server
gmtwhich [ERROR]: File earth_day_01d_p.tif not found!
gmtwhich [DEBUG]: GMT_End_IO: Output resource access is now disabled
gmtwhich [DEBUG]: gmtlib_unregister_io: Unregistering object no 0 [n_objects = 0]
gmt [DEBUG]: Entering GMT_Destroy_Session
```

But with GMT 6.5.0, `gmt which @earth_day_01d_p` works fine.

Also, I noticed that the internal data structure of the Blue/Black Marble images have changed from a 1-band ColorInterp/Color Table structure to a 3-band structure:

```diff
diff --git a/gdalinfo_earth_day b/gdalinfo_earth_day
index 75e7bbc91..02d818804 100644
--- a/gdalinfo_earth_day
+++ b/gdalinfo_earth_day
@@ -1,5 +1,5 @@
Driver: GTiff/GeoTIFF
-Files: earth_day_01d_p.tif
+Files: ~/.gmt/cache/earth_day_01d_p.tif
Size is 360, 180
Coordinate System is:
GEOGCRS["unknown",
@@ -26,269 +26,40 @@ Metadata:
AREA_OR_POINT=Area
Image Structure Metadata:
COMPRESSION=DEFLATE
- INTERLEAVE=BAND
- PREDICTOR=2
+ INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left (-180.0000000, 90.0000000) (180d 0' 0.00"W, 90d 0' 0.00"N)
Lower Left (-180.0000000, -90.0000000) (180d 0' 0.00"W, 90d 0' 0.00"S)
Upper Right ( 180.0000000, 90.0000000) (180d 0' 0.00"E, 90d 0' 0.00"N)
Lower Right ( 180.0000000, -90.0000000) (180d 0' 0.00"E, 90d 0' 0.00"S)
Center ( 0.0000000, 0.0000000) ( 0d 0' 0.01"E, 0d 0' 0.01"N)
-Band 1 Block=360x22 Type=Byte, ColorInterp=Palette
- Color Table (RGB with 256 entries)
- 0: 248,224,168,255
- 1: 240,224,152,255
- 2: 104,104,96,255
- 3: 16,24,56,255
- 4: 24,28,24,255
- 5: 104,80,48,255
- 6: 220,224,228,255
- 7: 48,56,32,255
- 8: 184,192,176,255
- 9: 104,104,40,255
- 10: 16,48,8,255
- 11: 96,96,56,255
- 12: 188,184,184,255
- 13: 128,112,60,255
- 14: 48,72,24,255
- 15: 8,16,48,255
- 16: 216,200,192,255
- 17: 80,80,28,255
- 18: 56,48,44,255
- 19: 72,88,24,255
- 20: 204,168,140,255
- 21: 128,136,136,255
- 22: 72,68,40,255
- 23: 144,120,68,255
- 24: 144,144,136,255
- 25: 88,80,48,255
- 26: 168,160,152,255
- 27: 88,104,40,255
- 28: 8,16,32,255
- 29: 168,116,84,255
- 30: 120,100,48,255
- 31: 200,192,184,255
- 32: 176,168,160,255
- 33: 136,112,80,255
- 34: 204,204,200,255
- 35: 184,152,124,255
- 36: 96,76,48,255
- 37: 88,72,48,255
- 38: 184,196,192,255
- 39: 28,56,48,255
- 40: 92,100,124,255
- 41: 184,176,176,255
- 42: 160,160,152,255
- 43: 132,144,144,255
- 44: 208,192,184,255
- 45: 128,100,64,255
- 46: 72,100,24,255
- 47: 36,48,16,255
- 48: 140,140,80,255
- 49: 152,144,136,255
- 50: 56,64,16,255
- 51: 168,168,168,255
- 52: 224,200,144,255
- 53: 176,176,168,255
- 54: 80,88,28,255
- 55: 152,144,144,255
- 56: 156,148,84,255
- 57: 160,160,160,255
- 58: 16,16,48,255
- 59: 168,176,168,255
- 60: 216,200,176,255
- 61: 16,8,48,255
- 62: 72,80,24,255
- 63: 132,140,124,255
- 64: 88,80,40,255
- 65: 152,152,176,255
- 66: 16,16,56,255
- 67: 20,48,24,255
- 68: 200,200,192,255
- 69: 56,48,72,255
- 70: 40,56,24,255
- 71: 120,136,56,255
- 72: 152,160,152,255
- 73: 8,8,24,255
- 74: 192,184,176,255
- 75: 248,244,172,255
- 76: 116,124,136,255
- 77: 88,68,40,255
- 78: 64,72,32,255
- 79: 172,180,176,255
- 80: 176,152,132,255
- 81: 24,40,24,255
- 82: 60,100,24,255
- 83: 168,148,128,255
- 84: 176,132,88,255
- 85: 200,192,192,255
- 86: 76,76,48,255
- 87: 152,116,80,255
- 88: 8,16,60,255
- 89: 152,152,144,255
- 90: 240,216,152,255
- 91: 52,80,32,255
- 92: 20,24,40,255
- 93: 132,144,156,255
- 94: 88,88,48,255
- 95: 20,32,8,255
- 96: 84,68,28,255
- 97: 172,164,180,255
- 98: 152,152,152,255
- 99: 120,112,56,255
- 100: 88,88,40,255
- 101: 56,80,8,255
- 102: 80,80,40,255
- 103: 176,176,160,255
- 104: 48,56,8,255
- 105: 104,84,68,255
- 106: 48,120,76,255
- 107: 184,176,168,255
- 108: 108,96,56,255
- 109: 232,224,212,255
- 110: 16,16,40,255
- 111: 96,88,48,255
- 112: 144,152,144,255
- 113: 104,112,68,255
- 114: 220,180,148,255
- 115: 28,32,60,255
- 116: 56,72,8,255
- 117: 104,96,40,255
- 118: 56,72,24,255
- 119: 24,64,24,255
- 120: 148,164,160,255
- 121: 180,176,140,255
- 122: 216,208,196,255
- 123: 156,128,92,255
- 124: 72,84,40,255
- 125: 56,80,16,255
- 126: 72,72,24,255
- 127: 48,44,12,255
- 128: 124,108,96,255
- 129: 64,80,24,255
- 130: 132,136,148,255
- 131: 200,200,184,255
- 132: 120,100,68,255
- 133: 16,28,24,255
- 134: 144,144,144,255
- 135: 116,120,124,255
- 136: 248,224,184,255
- 137: 184,184,168,255
- 138: 72,80,32,255
- 139: 152,148,160,255
- 140: 56,76,44,255
- 141: 232,208,144,255
- 142: 176,168,168,255
- 143: 104,96,88,255
- 144: 60,56,32,255
- 145: 168,152,92,255
- 146: 184,184,176,255
- 147: 152,144,124,255
- 148: 232,180,120,255
- 149: 208,204,192,255
- 150: 152,152,128,255
- 151: 188,180,108,255
- 152: 48,56,16,255
- 153: 28,60,40,255
- 154: 56,64,24,255
- 155: 160,152,144,255
- 156: 48,72,8,255
- 157: 168,160,160,255
- 158: 228,228,184,255
- 159: 48,64,8,255
- 160: 160,152,152,255
- 161: 148,112,64,255
- 162: 32,48,8,255
- 163: 80,68,40,255
- 164: 132,140,100,255
- 165: 84,104,28,255
- 166: 36,48,28,255
- 167: 188,192,184,255
- 168: 168,168,160,255
- 169: 240,248,248,255
- 170: 60,52,24,255
- 171: 248,248,220,255
- 172: 36,36,8,255
- 173: 144,152,152,255
- 174: 32,64,8,255
- 175: 96,80,80,255
- 176: 72,140,148,255
- 177: 48,72,16,255
- 178: 200,184,176,255
- 179: 148,144,152,255
- 180: 136,140,136,255
- 181: 244,200,144,255
- 182: 180,200,212,255
- 183: 160,168,160,255
- 184: 40,64,8,255
- 185: 56,72,16,255
- 186: 48,56,24,255
- 187: 64,72,24,255
- 188: 176,184,168,255
- 189: 48,64,16,255
- 190: 104,116,56,255
- 191: 28,24,56,255
- 192: 132,124,136,255
- 193: 72,72,32,255
- 194: 80,88,40,255
- 195: 56,88,12,255
- 196: 236,204,184,255
- 197: 72,64,28,255
- 198: 64,84,32,255
- 199: 24,48,8,255
- 200: 88,80,84,255
- 201: 240,232,236,255
- 202: 148,100,60,255
- 203: 148,116,100,255
- 204: 160,144,140,255
- 205: 208,132,88,255
- 206: 36,32,24,255
- 207: 148,132,132,255
- 208: 52,84,24,255
- 209: 196,180,168,255
- 210: 204,188,140,255
- 211: 24,16,52,255
- 212: 104,120,40,255
- 213: 240,184,144,255
- 214: 72,88,32,255
- 215: 104,84,40,255
- 216: 60,52,16,255
- 217: 208,200,184,255
- 218: 32,56,8,255
- 219: 24,56,8,255
- 220: 160,168,152,255
- 221: 116,136,164,255
- 222: 204,196,172,255
- 223: 48,84,12,255
- 224: 88,128,80,255
- 225: 64,64,24,255
- 226: 248,244,192,255
- 227: 172,180,192,255
- 228: 144,144,60,255
- 229: 40,56,8,255
- 230: 76,72,88,255
- 231: 40,72,24,255
- 232: 196,180,160,255
- 233: 152,168,132,255
- 234: 64,88,24,255
- 235: 64,64,16,255
- 236: 40,48,8,255
- 237: 220,152,124,255
- 238: 92,84,28,255
- 239: 204,208,220,255
- 240: 104,128,96,255
- 241: 132,168,164,255
- 242: 40,76,8,255
- 243: 188,184,196,255
- 244: 56,76,80,255
- 245: 156,148,104,255
- 246: 244,240,156,255
- 247: 68,80,16,255
- 248: 28,64,80,255
- 249: 152,176,188,255
- 250: 132,84,56,255
- 251: 8,8,48,255
- 252: 8,8,56,255
- 253: 8,40,24,255
- 254: 8,72,96,255
- 255: 248,248,248,255
+Band 1 Block=360x7 Type=Byte, ColorInterp=Undefined
+ Min=10.000 Max=255.000
+ Minimum=10.000, Maximum=255.000, Mean=49.508, StdDev=65.299
+ NoData Value=0
+ Metadata:
+ STATISTICS_MAXIMUM=255
+ STATISTICS_MEAN=49.507654320988
+ STATISTICS_MINIMUM=10
+ STATISTICS_STDDEV=65.299010755209
+ STATISTICS_VALID_PERCENT=100
+Band 2 Block=360x7 Type=Byte, ColorInterp=Undefined
+ Min=10.000 Max=255.000
+ Minimum=10.000, Maximum=255.000, Mean=49.911, StdDev=62.129
+ NoData Value=0
+ Metadata:
+ STATISTICS_MAXIMUM=255
+ STATISTICS_MEAN=49.910941358025
+ STATISTICS_MINIMUM=10
+ STATISTICS_STDDEV=62.129078727248
+ STATISTICS_VALID_PERCENT=100
+Band 3 Block=360x7 Type=Byte, ColorInterp=Undefined
+ Min=10.000 Max=255.000
+ Minimum=10.000, Maximum=255.000, Mean=65.605, StdDev=44.820
+ NoData Value=0
+ Metadata:
+ STATISTICS_MAXIMUM=255
+ STATISTICS_MEAN=65.605154320988
+ STATISTICS_MINIMUM=10
+ STATISTICS_STDDEV=44.819618148349
+ STATISTICS_VALID_PERCENT=100
```

Looking at https://oceania.generic-mapping-tools.org/gmt_data_server.txt, the modification date was 2023-09-29, and seems to be applied from https://github.com/GenericMappingTools/gmtserver-admin/commit/5bcc3d6190cf88f9ccdbb9ed3ca80451e94e61b2.

Just checking if these changes are expected. Personally, I prefer the new 3-band structure since it will simplify things in PyGMT (https://github.com/GenericMappingTools/pygmt/issues/1442#issuecomment-1341079313), but wanted to know if breaking the downloads for GMT 6.4.0 are ok.