gha/sync-release-branch: Add workflows write permission

Without it GitHub rejects the push:

```
refusing to allow a GitHub App to create or update workflow `.github/workflows/build.yml` without `workflows` permission
```

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

.github/workflows/sync-release-branch.yml

@@ -29,6 +29,7 @@ jobs:
     runs-on: ubuntu-24.04
     permissions:
       contents: write
+      workflows: write
     outputs:
       base_sha: ${{ steps.sync.outputs.base_sha }}
       has_changes: ${{ steps.sync.outputs.has_changes }}
@@ -119,6 +120,7 @@ jobs:
     environment: docker-releases
     permissions:
       contents: write
+      workflows: write
     timeout-minutes: 10
     steps:
       - name: Checkout