ci: Run coverage tests in parallel

[aborgna-q]

Instead of re-running the same tests again after the checks have finished,
run the coverage tests in parallel with the required check.

Also use the latest supported python version for the latter, instead of running the tests twice with the minimum py version.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.48%. Comparing base (ee40284) to head (621b449).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #399      +/-   ##
==========================================
- Coverage   92.50%   92.48%   -0.02%     
==========================================
  Files          48       48              
  Lines        5178     5178              
==========================================
- Hits         4790     4789       -1     
- Misses        388      389       +1     

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