Replace pkg_resources in test_load

[musicinmybrain]

Replace pkg_resources.resource_filename with
importlib.resources.files. This removes an implicit dependency on setuptools (to which pkg_resources belongs); furthermore, the entire pkg_resources API is deprecated.

Regarding the switch from __file__ to __package__, see: python/importlib_resources#60

• Closes # (insert issue number) N/A, no issue filed
• Executed pre-commit run --all-files with no errors
• The change is fully covered by automated unit tests N/A, only test code is modified
• Documented in docs/ as appropriate N/A, no user-visible change
• Added an entry to the CHANGES file Do we really need a changelog entry for this?

[codspeed-hq]

CodSpeed Performance Report

Merging #1870 will not alter performance

_{Comparing musicinmybrain:setuptools-test (3f8a048) with master (f9e139e)}

Summary

✅ 439 untouched benchmarks

[hgrecco]

Thanks