Fix a typo in _ResultCollection class comments

[0x404]

What does this PR do?

Fixes #18530

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📚 Documentation preview 📚: https://pytorch-lightning--18534.org.readthedocs.build/en/18534/

[codecov]

Codecov Report

Merging #18534 (78af0e6) into master (e958c6f) will decrease coverage by 35%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #18534      +/-   ##
==========================================
- Coverage      85%      50%     -35%     
==========================================
  Files         427      419       -8     
  Lines       33381    33235     -146     
==========================================
- Hits        28310    16699   -11611     
- Misses       5071    16536   +11465