Fix windows classifier in testsuite

[IAlibay]

Fixes #

Changes made in this Pull Request:

PR Checklist

• Issue raised/referenced?
• Tests updated/added?
• Documentation updated/added?
• package/CHANGELOG file updated?
• Is your name in package/AUTHORS? (If it is not, add it!)

Developers Certificate of Origin

I certify that I can submit this code contribution as described in the Developer Certificate of Origin, under the MDAnalysis LICENSE.

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📚 Documentation preview 📚: https://mdanalysis--4958.org.readthedocs.build/en/4958/

[IAlibay]

No point waiting for tests, thanks @p-j-smith !

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.41%. Comparing base (59aae2c) to head (9ceb9d4).
Report is 22 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4958      +/-   ##
===========================================
- Coverage    93.42%   93.41%   -0.02%     
===========================================
  Files          177      189      +12     
  Lines        21859    22925    +1066     
  Branches      3078     3078              
===========================================
+ Hits         20422    21415     +993     
- Misses         986     1059      +73     
  Partials       451      451              

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