Fix mypy errors attributed to pytorch_lightning.loggers.comet

[jxtngx]

What does this PR do?

Fix mypy errors attributed to pytorch_lightning.loggers.comet for issue #13445

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[codecov]

Codecov Report

Merging #13689 (d55367a) into master (1b31039) will decrease coverage by 9%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #13689     +/-   ##
=========================================
- Coverage      86%      76%     -9%     
=========================================
  Files         328      328             
  Lines       25600    25601      +1     
=========================================
- Hits        21933    19560   -2373     
- Misses       3667     6041   +2374