Add PHP 8.5 to CI matrix

[maksimovic]

Add PHP 8.5 to the CI test matrix. All tests pass on 8.5 locally.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.25%. Comparing base (8b7073e) to head (00111a0).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master       #5   +/-   ##
=========================================
  Coverage     96.25%   96.25%           
  Complexity      297      297           
=========================================
  Files            17       17           
  Lines           614      614           
=========================================
  Hits            591      591           
  Misses           23       23           

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