Add check to skip push if image already exists

Author: ServerSideHannes

.github/workflows/docker-publish.yml

@@ -45,7 +45,30 @@ jobs:
             type=sha,prefix={{branch}}-,format=short
             type=semver,pattern={{version}}
 
+      - name: Check if image exists
+        id: check
+        if: github.event_name != 'pull_request'
+        continue-on-error: true
+        run: |
+          TAGS="${{ steps.meta.outputs.tags }}"
+          IMAGE_EXISTS=false
+
+          for TAG in $TAGS; do
+            echo "Checking if image exists: $TAG"
+            if docker manifest inspect $TAG > /dev/null 2>&1; then
+              echo "Image already exists: $TAG"
+              IMAGE_EXISTS=true
+            else
+              echo "Image does not exist: $TAG"
+              IMAGE_EXISTS=false
+              break
+            fi
+          done
+
+          echo "should_push=$([[ "$IMAGE_EXISTS" == "false" ]] && echo "true" || echo "false")" >> $GITHUB_OUTPUT
+
       - name: Build and push Docker image
+        if: github.event_name == 'pull_request' || steps.check.outputs.should_push == 'true'
         uses: docker/build-push-action@v6
         with:
           context: .
@@ -55,3 +78,8 @@ jobs:
           cache-from: type=gha
           cache-to: type=gha,mode=max
           platforms: linux/amd64,linux/arm64
+
+      - name: Image push skipped
+        if: github.event_name != 'pull_request' && steps.check.outputs.should_push != 'true'
+        run: |
+          echo "All image tags already exist in registry. Skipping build and push."