### 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
DM = DagModel
        key = "my_dag_id"
        session = settings.Session()
        with tempfile.NamedTemporaryFile() as f:
            session.add(DM(dag_id=key, fileloc=f.name))
            session.commit()
            dag_command.dag_delete(self.parser.parse_args(['dags', 'delete', key, '--yes']))
            assert session.query(DM).filter_by(dag_id=key).count() == 0
    def test_cli_list_jobs(self):
        args = self.parser.parse_args(['dags', 'list-jobs'])
        dag_command.dag_list_jobs(args)
    def test_dag_state(self):
        assert (
            dag_command.dag_state(
                self.parser.parse_args(['dags', 'state', 'example_bash_operator', DEFAULT_DATE.isoformat()])
            )
            is None
        )
    @mock.patch("airflow.cli.commands.dag_command.DebugExecutor")
    @mock.patch("airflow.cli.commands.dag_command.get_dag")
    def test_dag_test(self, mock_get_dag, mock_executor):