### 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
params: Optional[Dict] = None,
        access_control: Optional[Dict] = None,
        is_paused_upon_creation: Optional[bool] = None,
        jinja_environment_kwargs: Optional[Dict] = None,
        render_template_as_native_obj: bool = False,
        tags: Optional[List[str]] = None,
    ):
        from airflow.utils.task_group import TaskGroup
        self.user_defined_macros = user_defined_macros
        self.user_defined_filters = user_defined_filters
        self.default_args = copy.deepcopy(default_args or {})
        self.params = params or {}
        
        if 'params' in self.default_args:
            self.params.update(self.default_args['params'])
            del self.default_args['params']
        
        self.params = ParamsDict(self.params)
        if full_filepath:
            warnings.warn(
                "Passing full_filepath to DAG() is deprecated and has no effect",
                DeprecationWarning,
                stacklevel=2,
            )
        validate_key(dag_id)
        self._dag_id = dag_id
        if concurrency:
            
            warnings.warn(
                "The 'concurrency' parameter is deprecated. Please use 'max_active_tasks'.",