### 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
mock_render_dag.return_value.pipe.return_value = b"DOT_DATA"
        mock_proc = mock.MagicMock()
        mock_proc.returncode = 0
        mock_proc.communicate.return_value = (b"OUT", b"ERR")
        mock_popen.return_value.__enter__.return_value = mock_proc
        with contextlib.redirect_stdout(io.StringIO()) as temp_stdout:
            dag_command.dag_show(
                self.parser.parse_args(['dags', 'show', 'example_bash_operator', '--imgcat'])
            )
        out = temp_stdout.getvalue()
        mock_render_dag.return_value.pipe.assert_called_once_with(format='png')
        mock_proc.communicate.assert_called_once_with(b'DOT_DATA')
        assert "OUT" in out
        assert "ERR" in out
    @mock.patch("airflow.cli.commands.dag_command.DAG.run")
    def test_cli_backfill_depends_on_past(self, mock_run):
        """
        Test that CLI respects -I argument
        We just check we call dag.run() right. The behaviour of that kwarg is
        tested in test_jobs
        """
        dag_id = 'test_dagrun_states_deadlock'
        run_date = DEFAULT_DATE + timedelta(days=1)
        args = [
            'dags',
            'backfill',
            dag_id,