### Body

Currently `start_date` is mandatory parameter.
For DAGs with `schedule=None` we can relax this requirement as no scheduling calculation needed so the `start_date` parameter isn't used.

### Committer

- [X] I acknowledge that I am a maintainer/committer of the Apache Airflow project.
"""
        We check that has_import_error is false for dags
        being set to scheduler to create dagruns
        """
        dag = DAG(dag_id="test_dags", start_date=DEFAULT_DATE)
        EmptyOperator(task_id="dummy", dag=dag, owner="airflow")
        orm_dag = DagModel(
            dag_id=dag.dag_id,
            has_task_concurrency_limits=False,
            next_dagrun=DEFAULT_DATE,
            next_dagrun_create_after=DEFAULT_DATE + timedelta(days=1),
            is_active=True,
        )
        assert not orm_dag.has_import_errors
        session.add(orm_dag)
        session.flush()
        query, _ = DagModel.dags_needing_dagruns(session)