Adapt workflow to use ghcr.io

.github/workflows/docker-build-push-backend-container-on-tag.yml

@@ -11,21 +11,21 @@ env:
 jobs:
   build-and-push:
     # TODO: make this a matrix build like the web containers
-    runs-on: 
-      group: amd64-image-builders
+    runs-on: ubuntu:latest
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
 
     - name: Set up Docker Buildx
       uses: docker/setup-buildx-action@v3
 
-    - name: Login to Docker Hub
+    - name: Login to GitHub Container Registry
       uses: docker/login-action@v3
       with:
-        username: ${{ secrets.DOCKER_USERNAME }}
-        password: ${{ secrets.DOCKER_TOKEN }}
+        registry: ghcr.io
+        username: ${{ github.actor }}
+        password: ${{ secrets.GITHUB_TOKEN }}
 
     - name: Backend Image Docker Build and Push
       uses: docker/build-push-action@v5