Fix release-branch-manager failure caused by conflicting flat release branch

[Copilot]

The release-branch-manager job was failing with [remote rejected] (directory file conflict) when trying to push release/v3 (and release/v1, release/v2). An orphaned flat release branch existed in the repo — git stores branch refs as filesystem paths, so refs/heads/release (file) blocks creation of refs/heads/release/v3 (requires refs/heads/release to be a directory).

Changes

• .github/workflows/release.yml: Added a cleanup job that runs before github-action (via needs: cleanup) and deletes the conflicting flat release branch via the GitHub API. Handles both HTTP 404 and 422 gracefully so the step is a no-op if the branch doesn't exist.

jobs:
  cleanup:
    runs-on: ubuntu-latest
    steps:
      - name: Delete conflicting flat 'release' branch if it exists
        uses: actions/github-script@v6
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          script: |
            try {
              await github.rest.git.deleteRef({
                owner: context.repo.owner,
                repo: context.repo.repo,
                ref: 'heads/release'
              });
              core.info('Deleted conflicting "release" branch.');
            } catch (e) {
              if (e.status === 404 || e.status === 422) {
                core.info('No conflicting "release" branch found, skipping.');
              } else {
                throw e;
              }
            }

  github-action:
    needs: cleanup
    uses: cloudposse/.github/.github/workflows/shared-release-branches.yml@main
    secrets: inherit