ci: fix proxyd publish

Updates the github action to properly reference
the `proxyd` dockerfile. The logic is copied from
the canary publish github action.

.github/workflows/release.yml

@@ -194,8 +194,8 @@ jobs:
       - name: Build and push
         uses: docker/build-push-action@v2
         with:
-          context: ./go/proxyd
-          file: ./Dockerfile
+          context: .
+          file: ./go/proxyd/Dockerfile
           push: true
           tags: ethereumoptimism/proxyd:${{ needs.release.outputs.proxyd }},ethereumoptimism/proxyd:latest
           build-args: |