fix typing error for HfArgumentParser for Optional[bool] (#10672)

* fix typing error for TrainingArguments Optional[bool]

* updating equality check for Optional[bool]

src/transformers/hf_argparser.py

@@ -99,7 +99,7 @@ class HfArgumentParser(ArgumentParser):
                 kwargs["type"] = type(kwargs["choices"][0])
                 if field.default is not dataclasses.MISSING:
                     kwargs["default"] = field.default
-            elif field.type is bool or field.type is Optional[bool]:
+            elif field.type is bool or field.type == Optional[bool]:
                 if field.default is True:
                     self.add_argument(f"--no_{field.name}", action="store_false", dest=field.name, **kwargs)