[GraphBolt] Fix attribute error when testing fused_csc_sampling_grpah. (#6842)

Co-authored-by: Ubuntu <ubuntu@ip-172-31-0-133.us-west-2.compute.internal>

tests/python/pytorch/graphbolt/impl/test_fused_csc_sampling_graph.py

@@ -1108,7 +1108,7 @@ def test_temporal_sample_neighbors_homo(
         node_timestamp_attr_name="timestamp" if use_node_timestamp else None,
         edge_timestamp_attr_name="timestamp" if use_edge_timestamp else None,
     )
-    sampled_count = torch.diff(subgraph.node_pairs.indptr).tolist()
+    sampled_count = torch.diff(subgraph.sampled_csc.indptr).tolist()
     available_neighbors = _get_available_neighbors()
     for i, count in enumerate(sampled_count):
         if not replace:
@@ -1116,7 +1116,7 @@ def test_temporal_sample_neighbors_homo(
         else:
             expect_count = fanouts[0] if len(available_neighbors[i]) > 0 else 0
         assert count == expect_count
-    sampled_neighbors = torch.split(subgraph.node_pairs.indices, sampled_count)
+    sampled_neighbors = torch.split(subgraph.sampled_csc.indices, sampled_count)
     for i, neighbors in enumerate(sampled_neighbors):
         assert set(neighbors.tolist()).issubset(set(available_neighbors[i]))
 
@@ -1376,7 +1376,7 @@ def test_temporal_sample_neighbors_hetero(
     available_neighbors = _get_available_neighbors()
     sampled_count = [0] * homo_seeds.numel()
     sampled_neighbors = [[] for _ in range(homo_seeds.numel())]
-    for etype, csc in subgraph.node_pairs.items():
+    for etype, csc in subgraph.sampled_csc.items():
         stype, _, _ = etype_str_to_tuple(etype)
         ntype_offset = ntypes_to_offset[stype]
         dest_nodes = per_etype_destination_nodes[etype]