cleanup rdl.py, num_neighbors_dict only needs to be computed once (pyg-team#10321)

minor change, just noticed while playing around with it

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: puririshi98

examples/rdl.py

@@ -634,15 +634,16 @@ def main():
 
     print("Preparing data loaders...")
     loader_dict = {}
+    num_neighbors_dict = {
+        edge_type: args.num_neighbors
+        for edge_type in data.edge_types
+    }
+
     for split in ["train", "val", "test"]:
         table = task.get_table(split)
         print(f"Creating '{split}' dataloader with columns: "
               f"{list(table.df.columns)}")
         table_input = get_train_table_input(split_table=table, task=task)
-        num_neighbors_dict = {
-            edge_type: args.num_neighbors
-            for edge_type in data.edge_types
-        }
         loader_dict[split] = NeighborLoader(
             data=data,
             num_neighbors=num_neighbors_dict,