[johnpaulalex]

Description of changes

Make run_ctsm_py_tests.py glob for CTSM test files relative to its own location rather than caller's arbitrary cwd.

This feels similar to other current-dir-dependent code fixed in Issue #2167: run_ctsm_py_tests failures at os.getcwd().

Description of generative AI usage:
Google Antigravity was used to write the code and tests, followed by human-guided verification.

Specific notes

Contributors other than yourself, if any:

• None

CTSM issues resolved or otherwise addressed, if any:

• None

Any user interface changes (namelist or namelist defaults changes)?
None.

Testing planned or performed, if any:

• Tested running ./python/run_ctsm_py_tests -u from CTSM root dir, python/ dir, and src/ dir and verified it consistently collects all 35 tests.

Requirements before merge:

• I have followed the CTSM contribution guidelines.
• The code in this PR branch builds with no errors.
• The code in this PR branch runs with no errors. Briefly describe tested configuration(s): Python unit tests collection via pytest locally.
• This either (a) does not change answers, (b) it only changes answers at roundoff level, or (c) I have performed a scientific evaluation of the answer changes. Which?: (a)
• I have reviewed relevant parts of the CLM documentation Tech Note or User's Guide to determine if anything needs to be changed or added. If it does, describe: None needed.
• This PR either (a) does not create a need to update the documentation or (b) includes required documentation updates (see guidelines for contributing documentation). Which?: (a)

[ekluzek]

Always a good capability for scripts to be able to be launched anywhere.

[ekluzek]

@johnpaulalex ran testing, and this change is small and safe. So I'm merging to b4b-dev.