### 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/models/dag.py
warnings.warn(
            "`DAG.is_fixed_time_schedule()` is deprecated.",
            category=DeprecationWarning,
            stacklevel=2,
        )
        try:
            return not self.timetable._should_fix_dst
        except AttributeError:
            return True
    def following_schedule(self, dttm):
        """
        Calculates the following schedule for this dag in UTC.
        :param dttm: utc datetime
        :return: utc datetime
        """
        warnings.warn(
            "`DAG.following_schedule()` is deprecated. Use `DAG.next_dagrun_info(restricted=False)` instead.",
            category=DeprecationWarning,
            stacklevel=2,
        )
        data_interval = self.infer_automated_data_interval(timezone.coerce_datetime(dttm))
        next_info = self.next_dagrun_info(data_interval, restricted=False)
        if next_info is None:
            return None
        return next_info.data_interval.start
    def previous_schedule(self, dttm):