Fixes another issue in binary matthews corr coef

[SkafteNicki]

What does this PR do?

Fixes #1829

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--1863.org.readthedocs.build/en/1863/

[codecov]

Codecov Report

Merging #1863 (3049513) into master (372f22e) will decrease coverage by 37%.
The diff coverage is 100%.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #1863     +/-   ##
========================================
- Coverage      87%     50%    -37%     
========================================
  Files         258     258             
  Lines       14591   14591             
========================================
- Hits        12766    7337   -5429     
- Misses       1825    7254   +5429