### 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/cli/commands/dag_command.py
"""Unpauses a DAG"""
    set_is_paused(False, args)
def set_is_paused(is_paused, args):
    """Sets is_paused for DAG by a given dag_id"""
    dag = DagModel.get_dagmodel(args.dag_id)
    if not dag:
        raise SystemExit(f"DAG: {args.dag_id} does not exist in 'dag' table")
    dag.set_is_paused(is_paused=is_paused)
    print(f"Dag: {args.dag_id}, paused: {is_paused}")
def dag_show(args):
    """Displays DAG or saves it's graphic representation to the file"""
    dag = get_dag(args.subdir, args.dag_id)
    dot = render_dag(dag)
    filename = args.save
    imgcat = args.imgcat
    if filename and imgcat:
        raise SystemExit(
            "Option --save and --imgcat are mutually exclusive. "
            "Please remove one option to execute the command.",
        )
    elif filename:
        _save_dot_to_file(dot, filename)
    elif imgcat:
        _display_dot_via_imgcat(dot)
    else:
        print(dot.source)
def _display_dot_via_imgcat(dot: Dot):