[Bug] fix import and unit test (#25558)

Signed-off-by: Jonas M. Kübler <44084297+jmkuebler@users.noreply.github.com>

tests/v1/attention/test_attention_splitting.py

@@ -11,7 +11,7 @@ from vllm.v1.attention.backends.utils import (UBatchSlice,
                                               slice_query_start_locs,
                                               split_attn_metadata,
                                               split_decodes_and_prefills)
-from vllm.v1.worker.ubatch_utils import create_ubatch_slices
+from vllm.v1.worker.ubatch_splitting import create_ubatch_slices
 
 
 @pytest.fixture