Black format pytorch_lightning/core/hooks.py

[ananthsub]

What does this PR do?

Split out changes from #3563 to make that PR easier to review. This formats the file according to the Black formatter

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[codecov]

Codecov Report

Merging #3575 into master will decrease coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #3575   +/-   ##
======================================
- Coverage      91%     91%   -0%     
======================================
  Files         109     109           
  Lines        8010    8058   +48     
======================================
+ Hits         7275    7303   +28     
- Misses        735     755   +20     

[Borda]

This just brings collision to all open PRs...