Add black to PR template checklist

[The-Compiler]

Would've avoided one force push I had to do 🙂

(checklist not really applicable)

[codecov-io]

Codecov Report

Merging #248 (3c82148) into master (d40303b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #248   +/-   ##
=======================================
  Coverage   99.36%   99.36%           
=======================================
  Files          17       17           
  Lines         631      631           
=======================================
  Hits          627      627           
  Misses          4        4           

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[jendrikseipp]

Good idea, thanks!