### 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.
self,
        task_ids: Collection[str | tuple[str, int]] | None = None,
        start_date: datetime | None = None,
        end_date: datetime | None = None,
        only_failed: bool = False,
        only_running: bool = False,
        confirm_prompt: bool = False,
        include_subdags: bool = True,
        include_parentdag: bool = True,
        dag_run_state: DagRunState = DagRunState.QUEUED,