Add new column to dataset
### Describe the bug

```
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
[<ipython-input-9-bd197b36b6a0>](https://localhost:8080/#) in <cell line: 1>()
----> 1 dataset['train']['/workspace/data']

3 frames
[/usr/local/lib/python3.10/dist-packages/datasets/formatting/formatting.py](https://localhost:8080/#) in _check_valid_column_key(key, columns)
    518 def _check_valid_column_key(key: str, columns: List[str]) -> None:
    519     if key not in columns:
--> 520         raise KeyError(f"Column {key} not in the dataset. Current columns in the dataset: {columns}")
    521 
    522 

KeyError: "Column train not in the dataset. Current columns in the dataset: ['image', '/workspace/data']"
```

### Steps to reproduce the bug

please find the notebook for reference: https://colab.research.google.com/drive/10lZ_zLtU4itYVmIVTvIEVbjfOtCZaAZy?usp=sharing

### Expected behavior

add column to the dataset

### Environment info

colab pro