chore(deps): update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/backstage.yaml

@@ -39,7 +39,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Set Branch Name
       run: |
         DNS_ZONE="${{ inputs.dns_zone }}"