### 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.
"""
        Return a list of dates between the interval received as parameter using this dag's schedule interval.
        Returned dates can be used for execution dates.
        :param start_date: The start date of the interval.
        :param end_date: The end date of the interval. Defaults to ``timezone.utcnow()``.
        :return: A list of dates within the interval following the dag's schedule.
        """
        warnings.warn(
            "`DAG.get_run_dates()` is deprecated. Please use `DAG.iter_dagrun_infos_between()` instead.",
            category=RemovedInAirflow3Warning,
            stacklevel=2,
        )
        earliest = timezone.coerce_datetime(start_date)
        if end_date is None:
            latest = pendulum.now(timezone.utc)
        else:
            latest = timezone.coerce_datetime(end_date)
        return [info.logical_date for info in self.iter_dagrun_infos_between(earliest, latest)]
    def normalize_schedule(self, dttm):