### 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
:param ignore_task_deps: whether to ignore the task dependency
        :type ignore_task_deps: bool
        :param pool: pool to backfill
        :type pool: str
        :param delay_on_limit_secs:
        :param verbose:
        :type verbose: flag to whether display verbose message to backfill console
        :param conf: a dictionary which user could pass k-v pairs for backfill
        :type conf: dictionary
        :param rerun_failed_tasks: flag to whether to
                                   auto rerun the failed task in backfill
        :type rerun_failed_tasks: bool
        :param run_backwards: Whether to process the dates from most to least recent
        :type run_backwards bool
        :param args:
        :param kwargs:
        """
        self.dag = dag
        self.dag_id = dag.dag_id
        self.bf_start_date = start_date
        self.bf_end_date = end_date
        self.mark_success = mark_success
        self.donot_pickle = donot_pickle
        self.ignore_first_depends_on_past = ignore_first_depends_on_past
        self.ignore_task_deps = ignore_task_deps
        self.pool = pool
        self.delay_on_limit_secs = delay_on_limit_secs
        self.verbose = verbose
        self.conf = conf
        self.rerun_failed_tasks = rerun_failed_tasks