chore (ci): add CI for PHP 8.5 on 6.0 branch

[phil-davis]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.27%. Comparing base (b8a828d) to head (353d6e9).
⚠️ Report is 4 commits behind head on 6.0.

Additional details and impacted files

@@             Coverage Diff              @@
##                6.0     #267      +/-   ##
============================================
- Coverage     94.31%   94.27%   -0.05%     
  Complexity      260      260              
============================================
  Files            15       15              
  Lines           880      873       -7     
============================================
- Hits            830      823       -7     
  Misses           50       50              

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