Fix context of Docker image push workflow

Author: evroon

.github/workflows/publish_docker_image.yml

@@ -37,7 +37,7 @@ jobs:
       - name: Build and push Docker image
         uses: docker/build-push-action@ad44023a93711e3deb337508980b4b5e9bcdc5dc
         with:
-          context: .
+          context: backend
           push: true
           file: backend/Dockerfile
           tags: ${{ steps.meta.outputs.tags }}