### 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,
        execution_date: Optional[str] = None,
        run_id: Optional[str] = None,
        session: Optional[Session] = None,
    ):
        """
        Returns the dag run for a given execution date or run_id if it exists, otherwise
        none.
        :param execution_date: The execution date of the DagRun to find.
        :param run_id: The run_id of the DagRun to find.
        :param session:
        :return: The DagRun if found, otherwise None.
        """
        if not (execution_date or run_id):
            raise TypeError("You must provide either the execution_date or the run_id")
        query = session.query(DagRun)
        if execution_date:
            query = query.filter(DagRun.dag_id == self.dag_id, DagRun.execution_date == execution_date)
        if run_id:
            query = query.filter(DagRun.dag_id == self.dag_id, DagRun.run_id == run_id)
        return query.first()
    @provide_session
    def get_dagruns_between(self, start_date, end_date, session=None):