Fix: Run unit tests with phpunit/phpunit:^8.5.19

[localheinz]

This pull request

• runs unit tests on GitHub Actions with phpunit/phpunit:^8.5.19

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (352439f) 65.86% compared to head (2eace15) 65.86%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #406   +/-   ##
=========================================
  Coverage     65.86%   65.86%           
  Complexity       89       89           
=========================================
  Files            21       21           
  Lines           457      457           
=========================================
  Hits            301      301           
  Misses          156      156           

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