DAGs that have entires in `dag_version` but not in `serialized_dag` are never serialized

### Under which category would you file this issue? Airflow Core ### Apache Airflow version 3.1.6 (the source code seems the same at 3.2.2) ### What happened and how to reproduce it? in https://github.com/apache/airflow/blob/main/airflow-core/src/airflow/models/serialized_dag.py in the method `write_dag`, you have the following block: ``` if dag_version and not has_task_instances: # This is for dynamic DAGs that the hashes changes often. We should update # the serialized dag, the dag_version and the dag_code instead of a new version # if the dag_version is not associated with any task instances # Use direct UPDATE to avoid loading the full serialized DAG result = session.execute( update(cls) .where(cls.dag_version_id == dag_version.id) .values( { cls._data: new_serialized_dag._data, cls._data_compressed: new_serialized_dag._data_compressed, cls.dag_hash: new_serialized_dag.dag_hash, } ) ) if getattr(result, "rowcount", 0) == 0: # No rows updated - serialized DAG doesn't exist return False ``` This allows the following scenario to happen - you have the dag in `dag_version` without task instances, but not in `serialized_dag` - in which case the dag is never serialized. ### What you think should happen instead? the dag should be serialized if it is missing ### Operating System _No response_ ### Deployment Other ### Apache Airflow Provider(s) _No response_ ### Versions of Apache Airflow Providers _No response_ ### Official Helm Chart version Not Applicable ### Kubernetes Version _No response_ ### Helm Chart configuration _No response_ ### Docker Image customizations _No response_ ### Anything else? Context: I ran into this state while running a custom application on top of a…