### 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/jobs/backfill_job.py
dep_context=DepContext(ignore_depends_on_past=False),
                    session=session,
                    verbose=self.verbose,
                )
                != t.are_dependencies_met(
                    dep_context=DepContext(ignore_depends_on_past=True), session=session, verbose=self.verbose
                )
                for t in ti_status.deadlocked
            )
            if deadlocked_depends_on_past:
                err += (
                    'Some of the deadlocked tasks were unable to run because '
                    'of "depends_on_past" relationships. Try running the '
                    'backfill with the option '
                    '"ignore_first_depends_on_past=True" or passing "-I" at '
                    'the command line.'
                )
            err += '\nThese tasks have succeeded:\n'
            err += tabulate_ti_keys_set(ti_status.succeeded)
            err += '\n\nThese tasks are running:\n'
            err += tabulate_ti_keys_set(ti_status.running)
            err += '\n\nThese tasks have failed:\n'
            err += tabulate_ti_keys_set(ti_status.failed)
            err += '\n\nThese tasks are skipped:\n'
            err += tabulate_ti_keys_set(ti_status.skipped)
            err += '\n\nThese tasks are deadlocked:\n'
            err += tabulate_tis_set(ti_status.deadlocked)
        return err
    @provide_session
    def _execute_dagruns(self, dagrun_infos, ti_status, executor, pickle_id, start_date, session=None):