Fix do_eval default value in training_args.py (#11511)

* Fix do_eval default value in training_args.py

* Update PULL_REQUEST_TEMPLATE.md

src/transformers/training_args.py

@@ -322,7 +322,7 @@ class TrainingArguments:
     )
 
     do_train: bool = field(default=False, metadata={"help": "Whether to run training."})
-    do_eval: bool = field(default=None, metadata={"help": "Whether to run eval on the dev set."})
+    do_eval: bool = field(default=False, 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."})
     evaluation_strategy: IntervalStrategy = field(
         default="no",