promote the use of Python 3.8 instead of 3.7

[fabianegli]

3.7 is the next version to be deprecated (2023-06-27) - I think it makes sense to promote a version that will not be deprecated within months.

PR checklist

• This comment contains a description of changes (with reason)
• CHANGELOG.md is updated
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

[codecov]

Codecov Report

Merging #1971 (4b141d9) into dev (778fb69) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev    #1971   +/-   ##
=======================================
  Coverage   61.13%   61.13%           
=======================================
  Files          37       37           
  Lines        4678     4678           
=======================================
  Hits         2860     2860           
  Misses       1818     1818           

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