Setup jdk 21 for docker workflows

.github/workflows/docker.yml

@@ -1,31 +1,44 @@
 name: Create and publish a Docker image
 on:
   push:
-    tags:
-      - v*
+    branches: ['**']
+
 env:
   REGISTRY: ghcr.io
   IMAGE_NAME: ${{ github.repository }}
 
 jobs:
   build-and-push-image:
     runs-on: ubuntu-latest
+
     permissions:
       contents: read
       packages: write
+
     steps:
+
       - name: Checkout repository
         uses: actions/checkout@v4
+
+      - name: Setup JVM
+        uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: 21
+          cache: sbt
+
       - name: Log in to the Container registry
         uses: docker/login-action@65b78e6e13532edd9afa3aa52ac7964289d1a9c1
         with:
           registry: ${{ env.REGISTRY }}
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
+
       - name: Extract metadata (tags, labels) for Docker
         id: meta
         uses: docker/metadata-action@9ec57ed1fcdbf14dcef7dfbe97b2010124a938b7
         with:
           images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+
       - name: Build and push Docker image
         run: sbt --client backend/Docker/publish