Make `AutoFormer` work with previous torch version (#24357)

fix
Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>

src/transformers/models/autoformer/modeling_autoformer.py

@@ -23,6 +23,7 @@ from typing import List, Optional, Tuple, Union
 
 import numpy as np
 import torch
+import torch.utils.checkpoint
 from torch import nn
 
 from ...activations import ACT2FN