Align Mergify queue with required up-to-date branch protection

[Copilot]

Motivation/summary

GitHub branch protection (Require branches to be up to date before merging) is incompatible with draft/two-step queue checks in the current Mergify setup. This PR switches Mergify to in-place checks so queueing and merging evaluate the same conditions.

• Merge queue settings

  • Added merge_queue.max_parallel_checks: 1.
  • Set queue_rules.default.batch_size: 1.

• Single-phase CI gating

  • Replaced queue_rules.default.conditions with:
    • queue_conditions
    • merge_conditions
  • Kept both condition sets identical to avoid two-step CI behavior.

merge_queue:
  max_parallel_checks: 1

queue_rules:
  - name: default
    batch_size: 1
    queue_conditions: &required_checks
      - check-success=test (macos-latest)
      - or:
        - check-success=test (windows-2025)
        - check-success=test (windows-latest)
      - check-success=system-test
      - check-success=lint
      - check-success=CLA
    merge_conditions: *required_checks

Checklist

• Update CHANGELOG.asciidoc
• Documentation has been updated

For functional changes, consider:

• Is it observable through the addition of either logging or metrics?
• Is its use being published in telemetry to enable product improvement?
• Have system tests been added to avoid regression?

How to test these changes

Review .mergify.yml and confirm:

• merge_queue.max_parallel_checks is 1
• default queue rule batch_size is 1
• queue_conditions and merge_conditions are present and identical

Related issues

Branch protection + Mergify incompatibility reported in the “Mergify failed” issue context.

[mergify]

This pull request does not have a backport label. Could you fix it @Copilot? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8.19 is the label to automatically backport to the 8.19 branch.
• backport-9./d is the label to automatically backport to the 9./d branch. /d is the digit.
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[endorama]

I'm trusting @v1v review on correctness, approving to unblock

[mergify]

This pull request is now in conflicts. Could you fix it @Copilot? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b copilot/fix-mergify-failed upstream/copilot/fix-mergify-failed
git merge upstream/main
git push upstream copilot/fix-mergify-failed