[lisachenko]

What and why

Brings the merge-up workflow from #841 to 4.x. A workflow triggered by a push runs from the branch that was pushed, so .github/workflows/merge-up.yml has to be on 4.x before the cascade can start. After this, every push to 4.x opens or updates a chore: merge 4.x into master PR. CS, PHPStan and PHPUnit also run on pushes to 4.x.

The head is commit 3ff646c itself: the same commit master already contains through #841, and its parent is the current tip of 4.x. The commit is not duplicated.

Merge with "Create a merge commit". Squash or rebase would create a new commit, which the next merge-up PR would then bring into master as a duplicate.

Checklist

• The title follows Conventional Commits (type(scope): summary)
• Tests cover the change: n/a, CI config only
• composer check passes: unchanged code; the same commit passed CI on build!: open 5.x on master (PHP 8.5+, merge-up from 4.x) #841
• User-facing or breaking changes are in CHANGELOG.md: n/a

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Generated by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.60%. Comparing base (5d52481) to head (3ff646c).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##                4.x     #843   +/-   ##
=========================================
  Coverage     98.60%   98.60%           
  Complexity     2291     2291           
=========================================
  Files           131      131           
  Lines          5947     5947           
=========================================
  Hits           5864     5864           
  Misses           83       83           

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