fix leaking imports in minimal testing

tests/datasets/test_sampler.py

@@ -17,7 +17,10 @@ import logging
 
 import pytest
 import torch
-from datasets import Dataset
+
+pytest.importorskip("datasets", reason="datasets is required (install lerobot[dataset])")
+
+from datasets import Dataset  # noqa: E402
 
 from lerobot.datasets.io_utils import (
     hf_transform_to_torch,