Minor type annotation fix (#27276)

* Minor type annotation fix

* Trigger Build

src/transformers/training_args.py

@@ -1144,7 +1144,7 @@ class TrainingArguments:
             "help": "If True, use gradient checkpointing to save memory at the expense of slower backward pass."
         },
     )
-    gradient_checkpointing_kwargs: dict = field(
+    gradient_checkpointing_kwargs: Optional[dict] = field(
         default=None,
         metadata={
             "help": "Gradient checkpointing key word arguments such as `use_reentrant`. Will be passed to `torch.utils.checkpoint.checkpoint` through `model.gradient_checkpointing_enable`."