### 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
)
                )
            dagrun_infos = dagrun_infos[::-1]
        dagrun_info_count = len(dagrun_infos)
        if dagrun_info_count == 0:
            self.log.info("No run dates were found for the given dates and dag interval.")
            return
        
        pickle_id = None
        if not self.donot_pickle and self.executor_class not in (
            executor_constants.LOCAL_EXECUTOR,
            executor_constants.SEQUENTIAL_EXECUTOR,
            executor_constants.DASK_EXECUTOR,
        ):
            pickle = DagPickle(self.dag)
            session.add(pickle)
            session.commit()
            pickle_id = pickle.id
        executor = self.executor
        executor.job_id = "backfill"
        executor.start()
        ti_status.total_runs = dagrun_info_count  
        try:
            remaining_dates = ti_status.total_runs
            while remaining_dates > 0:
                dagrun_infos_to_process = [
                    dagrun_info
                    for dagrun_info in dagrun_infos
                    if dagrun_info.logical_date not in ti_status.executed_dag_run_dates
                ]