### 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
include_dependent_dags: bool,
        as_pk_tuple: bool,
        exclude_task_ids: Collection[str],
        session: Session,
        dag_bag: "DagBag" = None,
        recursion_depth: int = 0,
        max_recursion_depth: int = None,
        visited_external_tis: Set[Tuple[str, str, datetime]] = None,
    ) -> Union[Iterable[TaskInstance], Set[TaskInstanceKey]]:
        TI = TaskInstance
        
        
        
        #
        
        
        result: Set[TaskInstanceKey] = set()
        
        if as_pk_tuple:
            tis = session.query(TI.dag_id, TI.task_id, TI.run_id)
        else:
            tis = session.query(TaskInstance)
        tis = tis.join(TaskInstance.dag_run)
        if include_subdags:
            
            conditions = []
            for dag in self.subdags + [self]:
                conditions.append(
                    (TaskInstance.dag_id == dag.dag_id) & TaskInstance.task_id.in_(dag.task_ids)
                )