Migrate test action to setup-micromamba and fix upload-artifact

[clelange]

Following https://github.com/mamba-org/provision-with-micromamba?tab=readme-ov-file#example-2-micromamba-version-environment-file-false-channels

Also fixes upload-artifact https://github.com/actions/upload-artifact/tree/v4/?tab=readme-ov-file#not-uploading-to-the-same-artifact

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📚 Documentation preview 📚: https://hepdata-lib--249.org.readthedocs.build/en/249/

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2806dfe) 87.70% compared to head (49a29e2) 87.70%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #249   +/-   ##
=======================================
  Coverage   87.70%   87.70%           
=======================================
  Files           5        5           
  Lines        1082     1082           
  Branches      231      231           
=======================================
  Hits          949      949           
  Misses         93       93           
  Partials       40       40           

Flag	Coverage Δ
unittests-3.10	87.70% <ø> (ø)
unittests-3.6	87.39% <ø> (ø)
unittests-3.7	87.39% <ø> (ø)
unittests-3.8	87.52% <ø> (ø)
unittests-3.9	87.52% <ø> (ø)

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