chore (ci): add CI for PHP 8.5 on 5.1 branch

[phil-davis]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.72%. Comparing base (414fb2b) to head (23285c1).
⚠️ Report is 3 commits behind head on 5.1.

Additional details and impacted files

@@             Coverage Diff              @@
##                5.1     #141      +/-   ##
============================================
- Coverage     99.73%   99.72%   -0.01%     
- Complexity      109      118       +9     
============================================
  Files             7        7              
  Lines           375      365      -10     
============================================
- Hits            374      364      -10     
  Misses            1        1              

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