buildx setup + subdir usage?

.gitea/workflows/container.yml

@@ -23,6 +23,9 @@ jobs:
           echo "${{ secrets.DOCKER_KEY }}" > /certs/client/key.pem
           echo "${{ secrets.DOCKER_CA }}" > /certs/client/ca.pem
 
+      - name: Setup Docker Builds
+        uses: docker/setup-buildx-action@v3
+
       - name: Login to Gitea registry
         uses: docker/login-action@v2
         with:
@@ -33,7 +36,7 @@ jobs:
       - name: Build and push Postfix Container
         uses: docker/build-push-action@v2
         with:
-          context: postfix
+          context: "{{defaultContext}}:postfix"
           file: Dockerfile
           push: true
           tags: git.domainforge.de/public/postfix:latest