### 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
:param only_failed: Only clear failed tasks
        :type only_failed: bool
        :param only_running: Only clear running tasks.
        :type only_running: bool
        :param confirm_prompt: Ask for confirmation
        :type confirm_prompt: bool
        :param include_subdags: Clear tasks in subdags and clear external tasks
            indicated by ExternalTaskMarker
        :type include_subdags: bool
        :param include_parentdag: Clear tasks in the parent dag of the subdag.
        :type include_parentdag: bool
        :param dag_run_state: state to set DagRun to. If set to False, dagrun state will not
            be changed.
        :param dry_run: Find the tasks to clear but don't clear them.
        :type dry_run: bool
        :param session: The sqlalchemy session to use
        :type session: sqlalchemy.orm.session.Session
        :param dag_bag: The DagBag used to find the dags subdags (Optional)
        :type dag_bag: airflow.models.dagbag.DagBag
        :param exclude_task_ids: A set of ``task_id`` that should not be cleared
        :type exclude_task_ids: frozenset
        """
        if get_tis:
            warnings.warn(
                "Passing `get_tis` to dag.clear() is deprecated. Use `dry_run` parameter instead.",
                DeprecationWarning,
                stacklevel=2,
            )
            dry_run = True
        if recursion_depth: