Checks out master branch as a side effect

def create_git_action_for_new_collection(self, new_collection_id=None):
        """Checks out master branch as a side effect"""
        ga = self.create_git_action()
        assert new_collection_id is not None
        # id should have been sorted out by the caller
        self.register_doc_id(ga, new_collection_id)
        return ga, new_collection_id