Load a local dataset twice
## Describe the bug
Load a local "dataset" composed of two csv files twice.

## Steps to reproduce the bug
Put the two joined files in a repository named "Data".
Then in python:

import datasets as ds
ds.load_dataset('Data', data_files = {'file1.csv', 'file2.csv'})

## Expected results
Should give something like (because files have only one data row):
Title, clicks
Truc et astuce, 123
Machin, 12

## Actual results
Gives 
Title, clicks
Truc et astuce, 123
Machin, 12
Truc et astuce, 123
Machin, 12

## Environment info
[file1.csv](https://github.com/huggingface/datasets/files/8256322/file1.csv)
[file2.csv](https://github.com/huggingface/datasets/files/8256323/file2.csv)
- `datasets` version: 2.0.0
- Platform: Linux-5.4.0-65-generic-x86_64-with-glibc2.10
- Python version: 3.8.12
- PyArrow version: 7.0.0
- Pandas version: 1.4.1
Hi @caush, thanks for reporting:

In order to load local CSV files, you can use our "csv" loading script: https://huggingface.co/docs/datasets/loading#csv
```python
dataset = load_dataset("csv", data_files=["data/file1.csv", "data/file2.csv"])
```
OR:
```python
dataset = load_dataset("csv", data_dir="data")
```

Alternatively, you may also use:
```python
dataset = load_dataset("data")