ci: allow release branch to be protected.

The deploy key can be added to the bypass list for branch protection,
allowing the release branch to be protected from pushes from regular
users.

Based on:
https://github.com/orgs/community/discussions/25305#discussioncomment-10728028

Author: ericonr

.github/workflows/update-release.yml

@@ -14,6 +14,7 @@ jobs:
       - uses: actions/checkout@v4
         with:
           fetch-depth: 0
+          ssh-key: ${{ secrets.DEPLOY_KEY }}
       - name: Update release branch
         run: |
           git push origin ${{ github.ref_name }}:release