mv file into dir not working on Ubuntu 24

The test failures we see on Ubuntu 24 on GitHub, https://github.com/MetPX/sarrac/actions/runs/15786279634/job/44503274532?pr=213 also occur on an Ubuntu 24 VM.

e.g. for test_shim_copy_strip:
```
+ mv test_file dirthree

+ sleep 10

RESULT: BAD! missing expected {'rename': 1} for 152 move test_file into dirthree subdir
```

I don't see any log messages complaining about a not-implemented syscall.

`strace -f bash -c './shim_copy_strip.sh >shim_copy_strip.log 2>&1' > ../straceout.txt 2>&1`

~~shows that a message is not posted because some file is read only (I assume fd 3?)~~ (I realized that message was irrelevant)

```
[pid 969065] ioctl(0, TCGETS, 0x7ffdf14657a0) = -1 ENOTTY (Inappropriate ioctl for device)
[pid 969065] write(2, "SR_SHIMDEBUG 1 969065 0.0813928 ", 32) = 32
[pid 969065] write(2, "renameat2 test_file dirthree\n", 29) = 29
[pid 969065] write(2, "SR_SHIMDEBUG 1 969065 0.0814726 ", 32) = 32
[pid 969065] write(2, " renameorlink test_file dirthree"..., 33) = 33
[pid 969065] write(2, "SR_SHIMDEBUG 1 969065 0.0815551 ", 32) = 32
[pid 969065] write(2, " renameorlink using renameat2\n", 30) = 30

[pid 969065] renameat2(AT_FDCWD, "test_file", AT_FDCWD, "dirthree", RENAME_NOREPLACE) = -1 EEXIST (File exists)

[pid 969065] write(2, "SR_SHIMDEBUG 1 969065 0.0816729 ", 32) = 32
[pid 969065] write(2, " renameorlink test_file dirthree"..., 49) = 49

[pid 969065] openat(AT_FDCWD, "dirthree", O_RDONLY|O_PATH|O_DIRECTORY) = 3

[pid 969065] write(2, "SR_SHIMDEBUG 1 969065 0.0817986 ", 32) = 32
[pid 969065] write(2, "renameat2 test_file test_file\n", 30) = 30
[pid 969065] write(2, "SR_SHIMDEBUG 1 969065 0.0818994 ", 32) = 32
[pid 969065] write(2, " renameorlink test_file test_fil"..., 34) = 34
[pid 969065] write(2, "SR_SHIMDEBUG 1 969065 0.0819783 ", 32) = 32
[pid 969065] write(2, " renameorlink using renameat2\n", 30) = 30

[pid 969065] renameat2(AT_FDCWD, "test_file", 3, "test_file", RENAME_NOREPLACE) = 0

[pid 969065] write(2, "SR_SHIMDEBUG 9 969065 0.0821166 ", 32) = 32
[pid 969065] write(2, "srshim_initialize shim about to "..., 47) = 47
[pid 969065] newfstatat(AT_FDCWD, "/local/home/sarra/.config/sr3/credentials.conf", {st_mode=S_IFREG|0664, st_size=860, ...}, 0) = 0
[pid 969065] write(2, "SR_SHIMDEBUG 2 969065 0.0822546 ", 32) = 32
[pid 969065] write(2, "fopen /local/home/sarra/.config/"..., 55) = 55
[pid 969065] openat(AT_FDCWD, "/local/home/sarra/.config/sr3/credentials.conf", O_RDONLY) = 4
[pid 969065] fstat(4, {st_mode=S_IFREG|0664, st_size=860, ...}) = 0
[pid 969065] read(4, "amqp://root:removed@localhost\n\n"..., 4096) = 860
[pid 969065] fcntl(4, F_GETFL) = 0x8000 (flags O_RDONLY|O_LARGEFILE)
[pid 969065] write(2, "SR_SHIMDEBUG 5 969065 0.0824909 ", 32) = 32
[pid 969065] write(2, " fclose 0x5bf48ccdb2a0 fd=4 fdst"..., 52) = 52
[pid 969065] write(2, "SR_SHIMDEBUG 5 969065 0.0825713 ", 32) = 32

# this is fd 4, not fd 3, I don't think it's related
[pid 969065] write(2, " fclose NO POST read-only. fd=4\n", 32) = 32

[pid 969065] close(4) = 0
```

and the log shows `renameorlink test_file test_file`

```
SR_SHIMDEBUG 1 969065 0.0813928 renameat2 test_file dirthree SR_SHIMDEBUG 1 969065 0.0814726 renameorlink test_file dirthree
SR_SHIMDEBUG 1 969065 0.0815551 renameorlink using renameat2
SR_SHIMDEBUG 1 969065 0.0816729 renameorlink test_file dirthree failed, no post
SR_SHIMDEBUG 1 969065 0.0817986 renameat2 test_file test_file
SR_SHIMDEBUG 1 969065 0.0818994 renameorlink test_file test_file
SR_SHIMDEBUG 1 969065 0.0819783 renameorlink using renameat2
SR_SHIMDEBUG 9 969065 0.0821166 srshim_initialize shim about to sr_config_init
SR_SHIMDEBUG 2 969065 0.0822546 fopen /local/home/sarra/.config/sr3/credentials.conf r
SR_SHIMDEBUG 5 969065 0.0824909 fclose 0x5bf48ccdb2a0 fd=4 fdstat=100000, starting
SR_SHIMDEBUG 5 969065 0.0825713 fclose NO POST read-only. fd=4
```

Manually stracing `mv test_file dirthree` shows this (on Ubuntu 24):

```
renameat2(AT_FDCWD, "test_file", AT_FDCWD, "dirthree", RENAME_NOREPLACE) = -1 EEXIST (File exists)
openat(AT_FDCWD, "dirthree", O_RDONLY|O_PATH|O_DIRECTORY) = 3
renameat2(AT_FDCWD, "test_file", 3, "test_file", RENAME_NOREPLACE) = 0
```

On Ubuntu 22, it's a bit different:
```
renameat2(AT_FDCWD, "test_file", AT_FDCWD, "dirthree/", RENAME_NOREPLACE) = -1 EEXIST (File exists)
newfstatat(AT_FDCWD, "dirthree/", {st_mode=S_IFDIR|0755, st_size=157, ...}, 0) = 0
renameat2(AT_FDCWD, "test_file", AT_FDCWD, "dirthree/test_file", RENAME_NOREPLACE) = 0
```

So on Ubuntu 22, it's using AT_FDCWD as the old and new dir FDs, and renaming test_file to dirthree/test_file. On Ubuntu 24, it opens the destination directory (as FD 3) and renames from `AT_FDCWD test_file` to `FD 3 (=dirthree) test_file`.

```
int renameat2(int olddirfd, const char *oldpath,
int newdirfd, const char *newpath, unsigned int flags);
```

I think I have to add some more debug logging to figure out where libsr3shim is going wrong.