### 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)

tests/cli/commands/test_dag_command.py
'--local',
            '--start-date',
            run_date.isoformat(),
            '--ignore-first-depends-on-past',
        ]
        dag = self.dagbag.get_dag(dag_id)
        dag_command.dag_backfill(self.parser.parse_args(args), dag=dag)
        mock_run.assert_called_once_with(
            start_date=run_date,
            end_date=run_date,
            conf=None,
            delay_on_limit_secs=1.0,
            donot_pickle=False,
            ignore_first_depends_on_past=True,
            ignore_task_deps=False,
            local=True,
            mark_success=False,
            pool=None,
            rerun_failed_tasks=False,
            run_backwards=False,
            verbose=False,
        )
    @mock.patch("airflow.cli.commands.dag_command.DAG.run")
    def test_cli_backfill_depends_on_past_backwards(self, mock_run):
        """
        Test that CLI respects -B argument and raises on interaction with depends_on_past
        """
        dag_id = 'test_depends_on_past'
        start_date = DEFAULT_DATE + timedelta(days=1)
        end_date = start_date + timedelta(days=1)