[trainer] fix batch processing in PPO trainer (#7576)

Author: gechengze

src/llamafactory/train/ppo/trainer.py

@@ -241,9 +241,11 @@ def ppo_train(self, resume_from_checkpoint: Optional[str] = None) -> None:
             self.tokenizer.padding_side = "right"  # change padding side
             queries, responses, rewards = [], [], []
             for idx in range(0, self.config.batch_size, self.config.mini_batch_size):
-                mini_batch_queries, mini_batch_responses = self.get_inputs(
-                    batch[idx : idx + self.config.mini_batch_size]
-                )
+                mini_batch = {
+                    "input_ids": batch["input_ids"][idx : idx + self.config.mini_batch_size],
+                    "attention_mask": batch["attention_mask"][idx : idx + self.config.mini_batch_size]
+                }
+                mini_batch_queries, mini_batch_responses = self.get_inputs(mini_batch)
                 mini_batch_rewards = self.get_rewards(mini_batch_queries, mini_batch_responses)
                 queries.extend(mini_batch_queries)
                 responses.extend(mini_batch_responses)