This PR updates the schema to use the correct default value for `scope` in the GHA caching options. This should be effectively a no-op. From: https://docs.docker.com/build/cache/backends/gha/ <img width="892" alt="image" src="https://github.com/user-attachments/assets/690cde79-e30e-4085-81fd-1c9dc1c6d7e9" /> Closes #496