`load_dataset(...,save_infos=True)` not working without loading script
Also, once the README.md exists in the python environment it is used when loading another dataset in the same format (e.g. json) since it always resolves the path to the same directory.
The consequence here is any other dataset won't load because of infos mismatch.
To reproduce this aspect:
1. Do a `load_datasets(...,save_infos=True)` with one dataset without a loading script
2. Try to load another dataset without a loading script in the same format (e.g. json) but with a different schema 
### Describe the bug

It seems that saving a dataset infos back into the card file is not working for datasets without a loading script.

After tracking the problem a bit it looks like saving the infos uses `Builder.get_imported_module_dir()` as its destination directory.
Internally this is a call to `inspect.getfile()` but since the actual builder class used is dynamically created (cf. `datasets.load.configure_builder_class`) this method actually return te path to the parent builder class (e.g. `datasets.packaged_modules.json.JSON`). 



### Steps to reproduce the bug

1. Have a local dataset without any loading script
2. Make sure there are no dataset infos in the README.md
3. Load with `save_infos=True`
4. No change in the dataset README.md
5. A new README.md file is created in the directory of the parent builder class (e.g. for json in `.../site-packages/datasets/packaged_modules/json/README.md`)

### Expected behavior

The dataset README.md should be updated and no file should be created in the python environment.

### Environment info

- `datasets` version: 2.15.0
- Platform: Linux-6.2.0-37-generic-x86_64-with-glibc2.35
- Python version: 3.10.12
- `huggingface_hub` version: 0.19.4
- PyArrow version: 14.0.1
- Pandas version: 2.1.3
- `fsspec` version: 2023.6.0
