Fix typo in error message
I already suggested this typo fix:
- https://github.com/huggingface/datasets-server/pull/1371/files#r1230650727

while reviewing PR:
- #1371

And normally it was taken into account with commit:
- https://github.com/huggingface/datasets-server/pull/1371/commits/1c55c9e6d55e178062eb6b85c33e7c6e71dc13ec

However a subsequent force-push removed this commit:
- https://github.com/huggingface/datasets-server/compare/1c55c9e6d55e178062eb6b85c33e7c6e71dc13ec..d29012b12274ea9d58d3a6c3cdbb2dd64097f202
Fix typo in error message: I already suggested this typo fix:
- https://github.com/huggingface/datasets-server/pull/1371/files#r1230650727

while reviewing PR:
- #1371

And normally it was taken into account with commit:
- https://github.com/huggingface/datasets-server/pull/1371/commits/1c55c9e6d55e178062eb6b85c33e7c6e71dc13ec

However a subsequent force-push removed this commit:
- https://github.com/huggingface/datasets-server/compare/1c55c9e6d55e178062eb6b85c33e7c6e71dc13ec..d29012b12274ea9d58d3a6c3cdbb2dd64097f202