Prefer main when auto-merging into staging

[validbeck]

Summary

Updates the Merge main into staging workflow so conflicts resolve in favor of main instead of failing and leaving staging stuck.

• Uses git merge -X theirs (on staging, theirs = main)
• Falls back to git checkout --theirs for any paths Git still marks unmerged

Test plan

• Merge this PR to main
• Merge PR #1370 to unblock current staging
• Push a follow-up commit to main and confirm Merge main into staging succeeds without manual intervention

Made with Cursor

[github-actions]

Pull requests must include at least one of the required labels: internal, highlight, enhancement, bug, deprecation, documentation. Except for internal, pull requests must also include a description in the release notes section.

[github-actions]

PR Summary

This PR updates the GitHub Actions workflow responsible for merging changes from the main branch into staging. The merge step now uses a strategy that favors the main branch by running a merge with the '-X theirs' option. In case of merge conflicts, the script automatically resolves them by checking out the main branch's versions for the affected files, adding them, and committing the merge. This ensures that in the event of a conflict, the main branch's changes take precedence without manual intervention.

Test Suggestions

• Test the merge action by simulating a merge with conflicts to ensure that the conflict resolution correctly defaults to the main branch's version.
• Verify that the workflow logs appropriately show the warning message when conflicts are encountered.
• Ensure that the commit after conflict resolution contains the correct changes and that no unintended changes are applied.

[github-actions]

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[github-actions]

Lighthouse check results

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Commit SHA: 4d4609d