[GraphBolt] Update `_init_all_nodes_set` (#7168)

python/dgl/graphbolt/impl/ondisk_dataset.py

@@ -828,11 +828,18 @@ class OnDiskDataset(Dataset):
             )
             return None
         num_nodes = graph.num_nodes
+        dtype = graph.indices.dtype
         if isinstance(num_nodes, int):
-            return ItemSet(num_nodes, names="seed_nodes")
+            return ItemSet(
+                torch.tensor(num_nodes, dtype=dtype),
+                names="seed_nodes",
+            )
         else:
             data = {
-                node_type: ItemSet(num_node, names="seed_nodes")
+                node_type: ItemSet(
+                    torch.tensor(num_node, dtype=dtype),
+                    names="seed_nodes",
+                )
                 for node_type, num_node in num_nodes.items()
             }
             return ItemSetDict(data)