default to None for input_ids, fixes cugraph failures (#8394)

```
713E File "/opt/rapids/cugraph/python/cugraph-pyg/cugraph_pyg/loader/cugraph_node_loader.py", line 511, in __iter__ 
714E self.current_loader = EXPERIMENTAL__BulkSampleLoader(
715E File "/opt/rapids/cugraph/python/cugraph-pyg/cugraph_pyg/loader/cugraph_node_loader.py", line 151, in __init__ 
716E input_type, input_nodes = torch_geometric.loader.utils.get_input_nodes(
717E TypeError: get_input_nodes() missing 1 required positional argument: 'input_id'
```

torch_geometric/loader/utils.py

@@ -248,7 +248,7 @@ def filter_custom_store(
 def get_input_nodes(
     data: Union[Data, HeteroData, Tuple[FeatureStore, GraphStore]],
     input_nodes: Union[InputNodes, TensorAttr],
-    input_id: Optional[Tensor],
+    input_id: Optional[Tensor] = None,
 ) -> Tuple[Optional[str], Tensor, Optional[Tensor]]:
     def to_index(nodes, input_id) -> Tuple[Tensor, Optional[Tensor]]:
         if isinstance(nodes, Tensor) and nodes.dtype == torch.bool: