test: replace os.path with pathlib Path

[bearomorphism]

As title.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.98%. Comparing base (bc1542c) to head (db52ea8).
⚠️ Report is 1 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1835   +/-   ##
=======================================
  Coverage   97.98%   97.98%           
=======================================
  Files          60       60           
  Lines        2686     2686           
=======================================
  Hits         2632     2632           
  Misses         54       54           

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