Use proper build-push-action file arg

Author: ColinMcNeil

.github/workflows/extension.yml

@@ -30,5 +30,5 @@ jobs:
           platforms: linux/amd64,linux/arm64
           push: true
           tags: docker/labs-ai-tools-for-devs:${{ github.event.release.tag_name }}
-          dockerfile: src/extension/Dockerfile
+          file: src/extension/Dockerfile
           context: src/extension