test strange matplotlib CI behavior on windows

[cchwala]

investigating the CI error for windows found in #109

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.75%. Comparing base (627dd69) to head (cd0d1d4).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #110   +/-   ##
=======================================
  Coverage   98.75%   98.75%           
=======================================
  Files           7        7           
  Lines         723      723           
=======================================
  Hits          714      714           
  Misses          9        9           

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[cchwala]

I is unclear why the code that failed in #109 did not fail here.

Because I temporarily fixed the problem via df72f67 this PR can be closed now.