mask_history args verify valid

src/llamafactory/hparams/data_args.py

@@ -141,3 +141,6 @@ class DataArguments:
 
         if self.streaming and self.max_samples is not None:
             raise ValueError("`max_samples` is incompatible with `streaming`.")
+
+        if self.mask_history and self.train_on_prompt:
+            raise ValueError("`Train on the last turn only` does not support `train_on_prompt`.")