load_dataset is case sentitive?

### Describe the bug

load_dataset() function is case sensitive?

### Steps to reproduce the bug

The following two code, get totally different behavior.

1. load_dataset('mbzuai/bactrian-x','en')

2. load_dataset('MBZUAI/Bactrian-X','en')

### Expected behavior

Compare 1 and 2.
1 will download all 52 subsets, shell output:
```Downloading and preparing dataset json/MBZUAI--bactrian-X to xxx```
2 will only download single subset, shell output
```Downloading and preparing dataset bactrian-x/en to xxx```

### Environment info

Python 3.10.11
datasets Version: 2.11.0