Add return type annotation to PreTrainedModel.from_pretrained (#31869)

Update modeling_utils.py

Add return type annotation to PreTrainedModel.from_pretrained

src/transformers/modeling_utils.py

@@ -2832,7 +2832,7 @@ class PreTrainedModel(nn.Module, ModuleUtilsMixin, GenerationMixin, PushToHubMix
         revision: str = "main",
         use_safetensors: bool = None,
         **kwargs,
-    ):
+    ) -> "PreTrainedModel":
         r"""
         Instantiate a pretrained pytorch model from a pre-trained model configuration.