docs: def add_migrations(self, migrations):
          """
          Add migrations to be applied.
  
          Args:
              migrations: a list of migrations to add of the form [(app, migration_name), ...]
          Raises:
              MigrationSessionError if called on a closed MigrationSession
          """
          if self.__closed:
              raise MigrationSessionError("Can't change applied session")
          self._to_apply.extend(migrations)