Don't use store_xxx on optional bools (#7786)

* Don't use `store_xxx` on optional bools

* Refine test

* Refine test

src/transformers/training_args.py

@@ -191,7 +191,7 @@ class TrainingArguments:
     do_eval: bool = field(default=None, metadata={"help": "Whether to run eval on the dev set."})
     do_predict: bool = field(default=False, metadata={"help": "Whether to run predictions on the test set."})
     evaluate_during_training: bool = field(
-        default=None,
+        default=False,
         metadata={"help": "Run evaluation during training at each logging step."},
     )
     evaluation_strategy: EvaluationStrategy = field(