### 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)

tests/cli/commands/test_dag_command.py
#
#
#
import contextlib
import io
import os
import tempfile
import unittest
from datetime import datetime, timedelta
from unittest import mock
import pytest
from airflow import settings
from airflow.cli import cli_parser
from airflow.cli.commands import dag_command
from airflow.exceptions import AirflowException
from airflow.models import DagBag, DagModel, DagRun
from airflow.utils import timezone
from airflow.utils.session import create_session
from airflow.utils.state import State
from airflow.utils.types import DagRunType
from tests.test_utils.config import conf_vars
from tests.test_utils.db import clear_db_dags, clear_db_runs
dag_folder_path = '/'.join(os.path.realpath(__file__).split('/')[:-1])
DEFAULT_DATE = timezone.make_aware(datetime(2015, 1, 1), timezone=timezone.utc)
TEST_DAG_FOLDER = os.path.join(os.path.dirname(dag_folder_path), 'dags')
TEST_DAG_ID = 'unit_tests'
EXAMPLE_DAGS_FOLDER = os.path.join(
    os.path.dirname(os.path.dirname(os.path.dirname(os.path.realpath(__file__)))), "airflow/example_dags"
)
class TestCliDags(unittest.TestCase):