bump minimum python version from 3.8 to 3.9

[dennisbader]

Checklist before merging this PR:

• Mentioned all issues that this PR fixes or addresses.
• Summarized the updates of this PR under Summary.
• Added an entry under Unreleased in the Changelog.

Summary

• bump minimum required python version from 3.8 to 3.9

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.87%. Comparing base (395efc8) to head (0dd6b52).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2586      +/-   ##
==========================================
- Coverage   93.89%   93.87%   -0.03%     
==========================================
  Files         139      139              
  Lines       14888    14888              
==========================================
- Hits        13979    13976       -3     
- Misses        909      912       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.