Fix AutoModel typing Import Error (#13178)

Fix typing import by converting to Python 3.9+ style type hint

Author: dg845

src/diffusers/models/auto_model.py

@@ -36,9 +36,7 @@ def __init__(self, *args, **kwargs):
         )
 
     @classmethod
-    def from_config(
-        cls, pretrained_model_name_or_path_or_dict: Optional[Union[str, os.PathLike, dict]] = None, **kwargs
-    ):
+    def from_config(cls, pretrained_model_name_or_path_or_dict: str | os.PathLike | dict | None = None, **kwargs):
         r"""
         Instantiate a model from a config dictionary or a pretrained model configuration file with random weights (no
         pretrained weights are loaded).