Fix MetricCollection compatibility with torch.jit.script

[SkafteNicki]

What does this PR do?

Fixes #2812

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• Did you write any new necessary tests?

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📚 Documentation preview 📚: https://torchmetrics--2813.org.readthedocs.build/en/2813/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69%. Comparing base (5d6bb56) to head (15b9f17).
Report is 1 commits behind head on master.

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #2813   +/-   ##
======================================
  Coverage      69%     69%           
======================================
  Files         344     344           
  Lines       18823   18824    +1     
======================================
+ Hits        12970   12971    +1     
  Misses       5853    5853