fix: workflow to build docker image

.github/workflows/copybara-docker.yml

@@ -56,24 +56,21 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ github.token }}
 
-      - name: Use working Dockerfile
-        run: curl -s https://raw.githubusercontent.com/google/copybara/master/Dockerfile > Dockerfile
-
       - name: Build and push
         uses: docker/build-push-action@v2
         with:
-          context: .
+          context: copybara
+          file: copybara/Dockerfile
           platforms: linux/amd64,linux/arm64
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
 
-      # Experimental
       - name: Install Cosign
         uses: sigstore/cosign-installer@main
 
       - name: Sign the image with GitHub OIDC **EXPERIMENTAL**
         run: cosign sign --oidc-issuer https://token.actions.githubusercontent.com ${TAGS}
         env:
           COSIGN_EXPERIMENTAL: 1
-          TAGS: ${{ steps.meta.outputs.tags }}
+          TAGS: ${{ steps.meta.outputs.tags }}