Use Python 3.9 syntax in examples (#37279)

Signed-off-by: cyy <cyyever@outlook.com>

examples/legacy/seq2seq/seq2seq_trainer.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from typing import Any, Dict, List, Optional, Tuple, Union
+from typing import Any, Optional, Union
 
 import torch
 from torch import nn
@@ -172,10 +172,10 @@ class Seq2SeqTrainer(Trainer):
     def prediction_step(
         self,
         model: nn.Module,
-        inputs: Dict[str, Union[torch.Tensor, Any]],
+        inputs: dict[str, Union[torch.Tensor, Any]],
         prediction_loss_only: bool,
-        ignore_keys: Optional[List[str]] = None,
-    ) -> Tuple[Optional[float], Optional[torch.Tensor], Optional[torch.Tensor]]:
+        ignore_keys: Optional[list[str]] = None,
+    ) -> tuple[Optional[float], Optional[torch.Tensor], Optional[torch.Tensor]]:
         """
         Perform an evaluation step on :obj:`model` using obj:`inputs`.