Fix changed files filters in tests workflow

[ricardoV94]

The paths filter action syntax is different than the githubs action one, so that pymc/**.py only matches python files in the first subdirectory, whereas the github one matched files in any subdirectories.

We need to use pymc/**/*.py instead.

The tests in #6658 were not triggered because of this

---

📚 Documentation preview 📚: https://pymc--6659.org.readthedocs.build/en/6659/

[codecov]

Codecov Report

Merging #6659 (7cd51a8) into main (0d7413e) will decrease coverage by 0.02%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6659      +/-   ##
==========================================
- Coverage   91.99%   91.97%   -0.02%     
==========================================
  Files          94       94              
  Lines       15942    15942              
==========================================
- Hits        14666    14663       -3     
- Misses       1276     1279       +3     

see 1 file with indirect coverage changes