### Apache Airflow version

2.2.0b2 (beta snapshot)

### Operating System

ubuntu 20.04

### Versions of Apache Airflow Providers

n/a

### Deployment

Virtualenv installation

### Deployment details

pip install /path/to/airflow/src

### What happened

Given any DAG initialized with: `schedule_interval=None`

Run `airflow dags test mydagname $(date +%Y-%m-%d)` and get an error:

```
INFO - No run dates were found for the given dates and dag interval.
```

This behavior changed in https://github.com/apache/airflow/pull/15397, it used to trigger a backfill dagrun at the given date.

### What you expected to happen

I expected a backfill dagrun with the given date, regardless of whether it fit into the `schedule_interval`.

If AIP-39 made that an unrealistic expectation, then I'd hope for some way to define unscheduled dags which can still be tested from the command line (which, so far as I know, is the fastest way to iterate on a DAG.).

As it is, I keep changing `schedule_interval` back and forth depending on whether I want to iterate via `astro dev start` (which tolerates `None` but does superfluous work if the dag is scheduled) or via `airflow dags test ...` (which doesn't tolerate `None`).

### How to reproduce

Initialize a DAG with: `schedule_interval=None` and run it via `airflow dags test mydagname $(date +%Y-%m-%d)`

### Anything else

_No response_

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

airflow/models/dag.py
self,
        task_ids=None,
        start_date=None,
        end_date=None,
        only_failed=False,
        only_running=False,
        confirm_prompt=False,
        include_subdags=True,
        include_parentdag=True,
        dag_run_state: DagRunState = DagRunState.QUEUED,
        dry_run=False,
        session=None,
        get_tis=False,
        recursion_depth=0,
        max_recursion_depth=None,
        dag_bag=None,
        exclude_task_ids: FrozenSet[str] = frozenset({}),
    ):
        """
        Clears a set of task instances associated with the current dag for
        a specified date range.
        :param task_ids: List of task ids to clear
        :type task_ids: List[str]
        :param start_date: The minimum execution_date to clear
        :type start_date: datetime.datetime or None
        :param end_date: The maximum execution_date to clear
        :type end_date: datetime.datetime or None