[2.12.0] DatasetDict.save_to_disk not saving to S3
### Describe the bug

When trying to save a `DatasetDict` to a private S3 bucket using `save_to_disk`, the artifacts are instead saved locally, and not in the S3 bucket.

I have tried using the deprecated `fs` as well as the `storage_options` arguments and I get the same results.

### Steps to reproduce the bug

1. Create a DatsetDict `dataset`
2. Create a S3FileSystem object
`s3 = datasets.filesystems.S3FileSystem(key=aws_access_key_id, secret=aws_secret_access_key)`
3. Save using `dataset_dict.save_to_disk(f"{s3_bucket}/{s3_dir}/{dataset_name}", storage_options=s3.storage_options)` or `dataset_dict.save_to_disk(f"{s3_bucket}/{s3_dir}/{dataset_name}", fs=s3)`
4. Check the corresponding S3 bucket and verify nothing has been uploaded
5. Check the path at f"{s3_bucket}/{s3_dir}/{dataset_name}" and verify that files have been saved there

### Expected behavior

Artifacts are uploaded at the f"{s3_bucket}/{s3_dir}/{dataset_name}" S3 location.

### Environment info

- `datasets` version: 2.12.0
- Platform: macOS-13.3.1-x86_64-i386-64bit
- Python version: 3.11.2
- Huggingface_hub version: 0.14.1
- PyArrow version: 12.0.0
- Pandas version: 2.0.1