fix save_model indent error in ppo trainer (#3450)

Co-authored-by: Yuanchen Xu <yuanchen.xu00@gmail.com>

applications/Chat/coati/trainer/ppo.py

@@ -117,6 +117,9 @@ class PPOTrainer(Trainer):
 
         return {'reward': experience.reward.mean().item()}
 
+    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)
@@ -129,7 +132,3 @@ def _set_default_generate_kwargs(strategy: Strategy, generate_kwargs: dict, acto
         new_kwargs['update_model_kwargs_fn'] = update_model_kwargs_fn
 
     return new_kwargs
-
-
-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)