Update Codecov action to v5

[RMeli]

Update codecov action from v4 to v5 (changes deprecated variables to new values).

I suspect that the fix for #4576 would be to switch to token-less access, but I need to understand this better.

PR Checklist

• Tests?
• Docs?
• CHANGELOG updated?
• Issue raised/referenced?

Developers certificate of origin

• I certify that this contribution is covered by the LGPLv2.1+ license as defined in our LICENSE and adheres to the Developer Certificate of Origin.

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📚 Documentation preview 📚: https://mdanalysis--4887.org.readthedocs.build/en/4887/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.63%. Comparing base (5eef341) to head (738a242).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4887      +/-   ##
===========================================
- Coverage    93.66%   93.63%   -0.03%     
===========================================
  Files          177      189      +12     
  Lines        21795    22861    +1066     
  Branches      3067     3067              
===========================================
+ Hits         20414    21407     +993     
- Misses         929     1002      +73     
  Partials       452      452              

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