Return a fully-qualified project_run string.

def project_run_path(cls, project, transfer_config, run):
        """Return a fully-qualified project_run string."""
        return google.api_core.path_template.expand(
            "projects/{project}/transferConfigs/{transfer_config}/runs/{run}",
            project=project,
            transfer_config=transfer_config,
            run=run,
        )