[montgomery_shenzhen] Fix use of split filename

src/ptbench/data/montgomery_shenzhen/datamodule.py

@@ -14,9 +14,9 @@ class DataModule(ConcatDataModule):
 
     def __init__(self, split_filename: str):
         montgomery_loader = MontgomeryLoader()
-        montgomery_split = make_montgomery_split("default.json")
+        montgomery_split = make_montgomery_split(split_filename)
         shenzhen_loader = ShenzhenLoader()
-        shenzhen_split = make_shenzhen_split("default.json")
+        shenzhen_split = make_shenzhen_split(split_filename)
 
         super().__init__(
             splits={