ValueError: Predictions and/or references don't match the expected format.

Getting this error when trying to compute IoU using the [Huggingface example](https://github.com/huggingface/evaluate/tree/main/metrics/mean_iou).
Flattening arrays does not solve the problem as [this issue](https://github.com/huggingface/evaluate/issues/392) suggests.

Steps to reproduce:
```
import numpy as np
import evaluate

mean_iou = evaluate.load("mean_iou")
predicted = np.array([[2, 2, 3], [8, 2, 4], [3, 255, 2]])
ground_truth = np.array([[1, 2, 2], [8, 2, 1], [3, 255, 1]])
results = mean_iou.compute(predictions=predicted, references=ground_truth, num_labels=10, ignore_index=255)
```

Using
evaluate 0.4.1
numpy 1.26.1

Full error:
```
Traceback (most recent call last):
File "/home/anba/catkin_ws/src/tas_dev/dev/anba/SAM/test.py", line 7, in
results = mean_iou.compute(predictions=predicted, references=ground_truth, num_labels=10, ignore_index=255)
File "/home/anba/anaconda3/envs/SAM/lib/python3.10/site-packages/evaluate/module.py", line 450, in compute
self.add_batch(**inputs)
File "/home/anba/anaconda3/envs/SAM/lib/python3.10/site-packages/evaluate/module.py", line 541, in add_batch
raise ValueError(error_msg) from None
ValueError: Predictions and/or references don't match the expected format.
Expected format: {'predictions': Sequence(feature=Sequence(feature=Value(dtype='uint16', id=None), length=-1, id=None), length=-1, id=None), 'references': Sequence(feature=Sequence(feature=Value(dtype='uint16', id=None), length=-1, id=None), length=-1, id=None)},
Input predictions: [ 2 2 3 8 2 4 3 255 2],
Input references: [ 1 2 2 8 2 1 3 255 1]
```