Enhancement: Run tests on PHP 8.1

[localheinz]

This pull request

• runs tests on PHP 8.1

[codecov]

Codecov Report

Merging #519 (5630656) into main (023caf0) will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##                main      #519   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity         7         7           
===========================================
  Files              2         2           
  Lines             26        26           
===========================================
  Hits              26        26           

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