Enhancement: Run tests on PHP 8.1

[localheinz]

This pull request

• runs tests on PHP 8.1

[codecov]

Codecov Report

Merging #808 (8189f96) into main (30430f3) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main     #808   +/-   ##
=========================================
  Coverage     83.96%   83.96%           
  Complexity       57       57           
=========================================
  Files             4        4           
  Lines           237      237           
=========================================
  Hits            199      199           
  Misses           38       38           

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