Fix eval hang (#9052)

* fix pipeline eval

* fix eval dataloader_num_workers

Author: gongel

paddlenlp/trainer/trainer.py

@@ -1500,15 +1500,15 @@ def get_eval_dataloader(self, eval_dataset: Optional[Dataset] = None) -> DataLoa
                     eval_dataset,
                     batch_sampler=eval_sampler,
                     collate_fn=self.data_collator,
-                    num_workers=self.args.dataloader_num_workers,
+                    num_workers=0,
                     eval=True,
                 )
             else:
                 return DataLoader(
                     eval_dataset,
                     batch_sampler=eval_sampler,
                     collate_fn=self.data_collator,
-                    num_workers=self.args.dataloader_num_workers,
+                    num_workers=0,
                 )
 
     def get_test_dataloader(self, test_dataset: Dataset) -> DataLoader: