Convert _VALID_DICT_FIELDS to class attribute for shared dict parsing in subclasses (#36736)

* make _VALID_DICT_FIELDS as a class attribute

* fix test case about TrainingArguments

tests/utils/test_hf_argparser.py

@@ -29,7 +29,6 @@ import yaml
 from transformers import HfArgumentParser, TrainingArguments
 from transformers.hf_argparser import make_choice_type_function, string_to_bool
 from transformers.testing_utils import require_torch
-from transformers.training_args import _VALID_DICT_FIELDS
 
 
 # Since Python 3.10, we can use the builtin `|` operator for Union types
@@ -412,7 +411,8 @@ class HfArgumentParserTest(unittest.TestCase):
         args = BasicExample(**args_dict_for_yaml)
         self.assertEqual(parsed_args, args)
 
-    def test_integration_training_args(self):
+    def test_z_integration_training_args(self):
+        # make sure that this test executes last in the test suite
         parser = HfArgumentParser(TrainingArguments)
         self.assertIsNotNone(parser)
 
@@ -424,7 +424,7 @@ class HfArgumentParserTest(unittest.TestCase):
         If this fails, a type annotation change is
         needed on a new input
         """
-        base_list = _VALID_DICT_FIELDS.copy()
+        base_list = TrainingArguments._VALID_DICT_FIELDS.copy()
         args = TrainingArguments
 
         # First find any annotations that contain `dict`
@@ -468,7 +468,7 @@ class HfArgumentParserTest(unittest.TestCase):
             self.assertIn(
                 field.name,
                 base_list,
-                f"Optional dict field `{field.name}` is not in the base list of valid fields. Please add it to `training_args._VALID_DICT_FIELDS`",
+                f"Optional dict field `{field.name}` is not in the base list of valid fields. Please add it to `TrainingArguments._VALID_DICT_FIELDS`",
             )
 
     @require_torch