### 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
"""Exclude tasks not included in the subdag from the given TaskGroup."""
            copied = copy.copy(group)
            copied.used_group_ids = set(copied.used_group_ids)
            copied._parent_group = parent_group
            copied.children = {}
            for child in group.children.values():
                if isinstance(child, BaseOperator):
                    if child.task_id in dag.task_dict:
                        copied.children[child.task_id] = dag.task_dict[child.task_id]
                    else:
                        copied.used_group_ids.discard(child.task_id)
                else:
                    filtered_child = filter_task_group(child, copied)
                    
                    if filtered_child.children:
                        copied.children[child.group_id] = filtered_child
            return copied
        dag._task_group = filter_task_group(self._task_group, None)
        
        
        subdag_task_groups = dag.task_group.get_task_group_dict()
        for group in subdag_task_groups.values():
            group.upstream_group_ids = group.upstream_group_ids.intersection(subdag_task_groups.keys())
            group.downstream_group_ids = group.downstream_group_ids.intersection(subdag_task_groups.keys())
            group.upstream_task_ids = group.upstream_task_ids.intersection(dag.task_dict.keys())
            group.downstream_task_ids = group.downstream_task_ids.intersection(dag.task_dict.keys())
        for t in dag.tasks: