use ghcr.io for backupimage (#6333)

* use ghcr.io for backup image

* backup script: use renamed script + improved build of image

---------

Co-authored-by: DerLinkman <niklas.meyer@servercow.de>

.github/workflows/rebuild_backup_image.yml

@@ -9,6 +9,8 @@ on:
 jobs:
   docker_image_build:
     runs-on: ubuntu-latest
+    permissions:
+      packages: write
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -19,17 +21,19 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
-      - name: Login to Docker Hub
+      - name: Login to GHCR
+        if: github.event_name != 'pull_request'
         uses: docker/login-action@v3
         with:
-          username: ${{ secrets.BACKUPIMAGEBUILD_ACTION_DOCKERHUB_USERNAME }}
-          password: ${{ secrets.BACKUPIMAGEBUILD_ACTION_DOCKERHUB_TOKEN }}
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Build and push
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@v5
         with:
           context: .
           platforms: linux/amd64,linux/arm64
           file: data/Dockerfiles/backup/Dockerfile
           push: true
-          tags: mailcow/backup:latest
+          tags: ghcr.io/mailcow/backup:latest