INFRA-3188:Create workflow to sync release, stable branches

[XxdpavelxX]

Ticket: https://consensyssoftware.atlassian.net/browse/INFRA-3188
Test stable sync branch: https://github.com/consensys-test/metamask-mobile-test-workflow/actions/runs/20148777729/job/57923961348, consensys-test/metamask-mobile-test-workflow#174

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Note

Adds a composite action and script to auto-create PRs syncing stable into active release/* branches after a release merges.

• CI/Automation:
  • New composite action /.github/actions/release-branch-sync/action.yml:
    • Inputs: merged-release-branch, github-token, optional github-tools-repository and github-tools-ref.
    • Checks out repo and tools, configures git user, runs sync script with env vars.
  • New script /.github/scripts/release-branch-sync.sh:
    • Detects active release branches from open PR titles matching release: X.Y.Z.
    • Skips invalid/older/merged/nonexistent branches and ones already up-to-date or with existing sync PRs.
    • Creates stable-sync-release-X.Y.Z branches from origin/stable, pushes, and opens PRs (head → release branch) via gh CLI with a templated body.
    • Includes logging, summary, and basic error handling.

^{Written by Cursor Bugbot for commit 9fad56f. This will update automatically on new commits. Configure here.}

[cursor]

Bug: Missing base branch filter when finding release PRs

The get_active_release_branches() function queries for PRs with titles matching "release: X.Y.Z" but doesn't filter by base branch. Release PRs merge release branches INTO stable, so the query at gh pr list is missing --base stable. This could incorrectly identify PRs targeting other branches (like main) as active release PRs if they happen to have a matching title format. Other scripts in the repository like get-release-timelines.sh correctly use --base stable when querying for release PRs.