### 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.default_args['start_date'] = timezone.convert_to_utc(self.default_args['start_date'])
        if 'end_date' in self.default_args:
            self.default_args['end_date'] = timezone.convert_to_utc(self.default_args['end_date'])
        
        if timetable is None:
            self.timetable = create_timetable(schedule_interval, self.timezone)
            if schedule_interval is ScheduleIntervalArgNotSet:
                schedule_interval = DEFAULT_SCHEDULE_INTERVAL
            self.schedule_interval: ScheduleInterval = schedule_interval
        elif schedule_interval is ScheduleIntervalArgNotSet:
            self.timetable = timetable
            self.schedule_interval = self.timetable.summary
        else:
            raise TypeError("cannot specify both 'schedule_interval' and 'timetable'")
        if isinstance(template_searchpath, str):
            template_searchpath = [template_searchpath]
        self.template_searchpath = template_searchpath
        self.template_undefined = template_undefined
        self.parent_dag: Optional[DAG] = None  
        self.last_loaded = timezone.utcnow()
        self.safe_dag_id = dag_id.replace('.', '__dot__')
        self.max_active_runs = max_active_runs
        self.dagrun_timeout = dagrun_timeout
        self.sla_miss_callback = sla_miss_callback
        if default_view in DEFAULT_VIEW_PRESETS:
            self._default_view: str = default_view
        else:
            raise AirflowException(
                f'Invalid values of dag.default_view: only support '
                f'{DEFAULT_VIEW_PRESETS}, but get {default_view}'