Calling shuffle on a IterableDataset with streaming=True, gives "ValueError: cannot reshape array"
### Describe the bug

When calling shuffle on a IterableDataset with streaming=True, I get the following error:

```
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/administrator/Documents/Projects/huggingface/jax-diffusers-sprint-consistency-models/virtualenv/lib/python3.10/site-packages/datasets/iterable_dataset.py", line 937, in __iter__
    for key, example in ex_iterable:
  File "/home/administrator/Documents/Projects/huggingface/jax-diffusers-sprint-consistency-models/virtualenv/lib/python3.10/site-packages/datasets/iterable_dataset.py", line 627, in __iter__
    for x in self.ex_iterable:
  File "/home/administrator/Documents/Projects/huggingface/jax-diffusers-sprint-consistency-models/virtualenv/lib/python3.10/site-packages/datasets/iterable_dataset.py", line 138, in __iter__
    yield from self.generate_examples_fn(**kwargs_with_shuffled_shards)
  File "/home/administrator/.cache/huggingface/modules/datasets_modules/datasets/mnist/fda16c03c4ecfb13f165ba7e29cf38129ce035011519968cdaf74894ce91c9d4/mnist.py", line 111, in _generate_examples
    images = np.frombuffer(f.read(), dtype=np.uint8).reshape(size, 28, 28)
ValueError: cannot reshape array of size 59992 into shape (60000,28,28)

```
Tested with the fashion_mnist and mnist datasets

### Steps to reproduce the bug

Code to reproduce
```python
from datasets import load_dataset

SHUFFLE_SEED = 42
SHUFFLE_BUFFER_SIZE = 10_000

dataset = load_dataset('fashion_mnist', streaming=True).shuffle(seed=SHUFFLE_SEED, buffer_size=SHUFFLE_BUFFER_SIZE)
next(iter(dataset['train']))
```

### Expected behavior

A random item from the dataset and no error

### Environment info

- `datasets` version: 2.11.0
- Platform: Linux-5.15.0-69-generic-x86_64-with-glibc2.35
- Python version: 3.10.6
- Huggingface_hub version: 0.13.4
- PyArrow version: 11.0.0
- Pandas version: 2.0.0

Hi! I've merged a PR on the Hub with a fix: https://huggingface.co/datasets/fashion_mnist/discussions/3 Thanks, this appears to have fixed the issue.

I've created a PR for the same change in the mnist dataset: https://huggingface.co/datasets/mnist/discussions/3/files