Error message could be in simpler English for incorrect syntax in test names

`./create_test SMS_L10d_D_Mmpi-serial.CLM_USRDAT.I1PtClm51Bgc.izumi_nag.clm-default--clm-NEON-NIWO`
gave me this error:
```
Finished XML for test SMS_L10d_D_Mmpi-serial.CLM_USRDAT.I1PtClm51Bgc.izumi_nag.clm-default--clm-NEON-NIWO in 0.232909 seconds (FAIL). [COMPLETED 1 of 1]
Case dir: /scratch/cluster/slevis/SMS_L10d_D_Mmpi-serial.CLM_USRDAT.I1PtClm51Bgc.izumi_nag.clm-default--clm-NEON-NIWO.20230627_133512_wvaqn7
Errors were:
Test 'SMS_L10d_D_Mmpi-serial.CLM_USRDAT.I1PtClm51Bgc.izumi_nag.clm-default--clm-NEON-NIWO' failed in phase 'XML' with exception ''NoneType' object has no attribute 'group''
File "/fs/cgd/data0/slevis/git/add_xs_ground_ice_pr1787/cime/CIME/test_scheduler.py", line 1093, in _run_catch_exceptions
return run(test)
File "/fs/cgd/data0/slevis/git/add_xs_ground_ice_pr1787/cime/CIME/test_scheduler.py", line 885, in _xml_phase
opt = match.group(1)
```

For the test to work, @ekluzek and I discovered that we needed to replace L10d with Ld10 in the test name.

Relates to https://github.com/ESCOMP/CTSM/issues/2043