Initialize aggregation metrics with default floating type

[SkafteNicki]

What does this PR do?

Fixes #2365

Before submitting

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• Did you make sure to update the docs?
• Did you write any new necessary tests?

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📚 Documentation preview 📚: https://torchmetrics--2366.org.readthedocs.build/en/2366/

[codecov]

Codecov Report

Merging #2366 (59bb3c9) into master (4527aaf) will not change coverage.
The diff coverage is 100%.

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #2366   +/-   ##
======================================
  Coverage      69%     69%           
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  Files         305     305           
  Lines       17164   17164           
======================================
  Hits        11836   11836           
  Misses       5328    5328