Schrödinger's dataset_dict
### Describe the bug

If you use load_dataset('json', data_files="path/test.json"), it will return DatasetDict({train:...}).

And if you use load_dataset("path"), it will return DatasetDict({test:...}).

Why can't the output behavior be unified?

### Steps to reproduce the bug

as description above.

### Expected behavior

consistent predictable output.

### Environment info

'2.11.0'