修复报错

backend/app/engines/text_engine.py

@@ -339,7 +339,7 @@ class TextEngine(BaseEngine):
                 ref_model=ref_model,
                 args=DPOConfig(**base_trainer_kwargs),
                 train_dataset=dataset,
-                tokenizer=self._tokenizer,
+                processing_class=self._tokenizer,
             )
 
             # 修复 Qwen tokenizer bug（TRL #1073）：