### 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
from airflow.utils import cli as cli_utils
from airflow.utils.cli import (
    get_dag,
    get_dag_by_file_location,
    process_subdir,
    sigint_handler,
    suppress_logs_and_warning,
)
from airflow.utils.dot_renderer import render_dag
from airflow.utils.session import create_session, provide_session
from airflow.utils.state import State
@cli_utils.action_logging
def dag_backfill(args, dag=None):
    """Creates backfill job or dry run for a DAG"""
    logging.basicConfig(level=settings.LOGGING_LEVEL, format=settings.SIMPLE_LOG_FORMAT)
    signal.signal(signal.SIGTERM, sigint_handler)
    import warnings
    warnings.warn(
        '--ignore-first-depends-on-past is deprecated as the value is always set to True',
        category=PendingDeprecationWarning,
    )
    if args.ignore_first_depends_on_past is False:
        args.ignore_first_depends_on_past = True
    dag = dag or get_dag(args.subdir, args.dag_id)
    if not args.start_date and not args.end_date:
        raise AirflowException("Provide a start_date and/or end_date")
    
    args.end_date = args.end_date or args.start_date
    args.start_date = args.start_date or args.end_date
    if args.task_regex: