Add PHP 8.6 to PHPUnit workflow

[mondrake]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.68%. Comparing base (257ab8a) to head (8cd53e8).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #103   +/-   ##
=========================================
  Coverage     97.68%   97.68%           
  Complexity      220      220           
=========================================
  Files             9        9           
  Lines           519      519           
=========================================
  Hits            507      507           
  Misses           12       12           

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