### 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
more information about the function signature and parameters that are
        passed to the callback.
    :type sla_miss_callback: callable
    :param default_view: Specify DAG default view (tree, graph, duration,
                                                   gantt, landing_times), default tree
    :type default_view: str
    :param orientation: Specify DAG orientation in graph view (LR, TB, RL, BT), default LR
    :type orientation: str
    :param catchup: Perform scheduler catchup (or only run latest)? Defaults to True
    :type catchup: bool
    :param on_failure_callback: A function to be called when a DagRun of this dag fails.
        A context dictionary is passed as a single parameter to this function.
    :type on_failure_callback: callable
    :param on_success_callback: Much like the ``on_failure_callback`` except
        that it is executed when the dag succeeds.
    :type on_success_callback: callable
    :param access_control: Specify optional DAG-level actions, e.g.,
        "{'role1': {'can_read'}, 'role2': {'can_read', 'can_edit'}}"
    :type access_control: dict
    :param is_paused_upon_creation: Specifies if the dag is paused when created for the first time.
        If the dag exists already, this flag will be ignored. If this optional parameter
        is not specified, the global config setting will be used.
    :type is_paused_upon_creation: bool or None
    :param jinja_environment_kwargs: additional configuration options to be passed to Jinja
        ``Environment`` for template rendering
        **Example**: to avoid Jinja from removing a trailing newline from template strings ::
            DAG(dag_id='my-dag',
                jinja_environment_kwargs={
                    'keep_trailing_newline': True,
                    # some other jinja2 Environment options here