[chat]fix save_model(#3377)

The function save_model should be a part of PPOTrainer.

applications/Chat/coati/trainer/ppo.py

@@ -120,6 +120,9 @@ class PPOTrainer(Trainer):
     def save_model(self, path: str, only_rank0: bool = False, tokenizer: Optional[PreTrainedTokenizerBase] = None) -> None:
         self.strategy.save_model(model=self.actor, path=path, only_rank0=only_rank0, tokenizer=tokenizer)
 
+    def save_model(self, path: str, only_rank0: bool = False, tokenizer: Optional[PreTrainedTokenizerBase] = None) -> None:
+        self.strategy.save_model(model=self.actor, path=path, only_rank0=only_rank0, tokenizer=tokenizer)
+
 
 def _set_default_generate_kwargs(strategy: Strategy, generate_kwargs: dict, actor: Actor) -> None:
     origin_model = strategy._unwrap_actor(actor)