Add build-context to docker buildx in publish step

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

Author: alexellis

.github/workflows/publish.yaml

@@ -36,6 +36,8 @@ jobs:
       - name: Push containers
         uses: docker/build-push-action@v2
         with:
+          context: .
+          file: ./Dockerfile
           outputs: "type=registry,push=true"
           platforms: linux/amd64,linux/arm/v7,linux/arm64
           tags: |