Previously, any errors in those files would e.g. blow up the update process in docker_manager.
Now it prints out an error and proceeds as if there was no compatibility file.
Includes:
* DEV: Extract setup_git_repo
* DEV: Use `Dir.mktmpdir`
* DEV: Default to `main` branch (The latest versions of git already do this, so to avoid problems do this by default)
