CI: Suit actions/setup-python@v4 new changing

[Zeroto521]

• closes BOT: Bump actions/setup-python from 3 to 4 #578
• whatsnew entry

actions/setup-python@v4 won't input python-version: "3.x" as default, actions/setup-python#433

[codecov]

Codecov Report

Merging #581 (af256ab) into main (68e04e3) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #581   +/-   ##
=======================================
  Coverage   99.55%   99.55%           
=======================================
  Files          75       75           
  Lines         904      904           
  Branches       99       99           
=======================================
  Hits          900      900           
  Misses          1        1           
  Partials        3        3           

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