Invoke subshell with the current python interpreter

[dirkmueller]

If tests are executed outside a virtualenv "python" might not be the python interpreter the tests are being invoked with

[codecov]

Codecov Report

Merging #252 (e2bf636) into main (1902bf1) will not change coverage.
Report is 1 commits behind head on main.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #252   +/-   ##
=======================================
  Coverage   53.36%   53.36%           
=======================================
  Files          11       11           
  Lines         832      832           
  Branches      168      168           
=======================================
  Hits          444      444           
  Misses        329      329           
  Partials       59       59           

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[Erotemic]

Looks good. Thanks for catching this!