fix imports

Author: ryankert01

python/ray/data/tests/test_execution_optimizer_limit_pushdown.py

@@ -7,6 +7,7 @@
 import ray
 from ray.data import Dataset
 from ray.data._internal.logical.interfaces import Plan
+from ray.data._internal.util import rows_same
 from ray.data.block import BlockMetadata
 from ray.data.datasource import Datasource
 from ray.data.datasource.datasource import ReadTask