add deepspeed check in PPO training

Former-commit-id: ed1c2c5557

src/llmtuner/tuner/ppo/trainer.py

@@ -39,6 +39,9 @@ class PPOPeftTrainer(PPOTrainer, PeftTrainer):
         **kwargs
     ):
         PPOTrainer.__init__(self, **kwargs)
+        if getattr(self.accelerator.state, "deepspeed_plugin", None) is not None:
+            raise ValueError("PPOTrainer is incompatible with DeepSpeed.")
+
         self.args = training_args
         self.finetuning_args = finetuning_args
         self.generating_args = generating_args