Fix resize_token_embeddings (#26861) (#26865)

* Fix `resize_token_embeddings` about `requires_grad`

The method `resize_token_embeddings` should keep `requires_grad`
unchanged for all parameters in embeddings.

Previously, `resize_token_embeddings` always set `requires_grad`
to `True`. After fixed, `resize_token_embeddings` copy the
`requires_grad` attribute in the old embeddings.

src/transformers/modeling_utils.py

@@ -1586,6 +1586,8 @@ def _resize_token_embeddings(self, new_num_tokens, pad_to_multiple_of=None):
         if hasattr(old_embeddings, "_hf_hook"):
             hook = old_embeddings._hf_hook
             add_hook_to_module(new_embeddings, hook)
+        old_embeddings_requires_grad = old_embeddings.weight.requires_grad
+        new_embeddings.requires_grad_(old_embeddings_requires_grad)
         self.set_input_embeddings(new_embeddings)
 
         # Update new_num_tokens with the actual size of new_embeddings
@@ -1605,6 +1607,8 @@ def _resize_token_embeddings(self, new_num_tokens, pad_to_multiple_of=None):
             if hasattr(old_lm_head, "_hf_hook"):
                 hook = old_lm_head._hf_hook
                 add_hook_to_module(new_lm_head, hook)
+            old_lm_head_requires_grad = old_lm_head.weight.requires_grad
+            new_lm_head.requires_grad_(old_lm_head_requires_grad)
             self.set_output_embeddings(new_lm_head)
 
         return self.get_input_embeddings()