Fix error in doc of `DataCollatorWithPadding` (#16662)

The defalut value of `padding` in `DataCollatorWithPadding` is `True`, not `False`.

src/transformers/data/data_collator.py

@@ -220,11 +220,11 @@ class DataCollatorWithPadding:
             Select a strategy to pad the returned sequences (according to the model's padding side and padding index)
             among:
 
-            - `True` or `'longest'`: Pad to the longest sequence in the batch (or no padding if only a single sequence
+            - `True` or `'longest'` (default): Pad to the longest sequence in the batch (or no padding if only a single sequence
               is provided).
             - `'max_length'`: Pad to a maximum length specified with the argument `max_length` or to the maximum
               acceptable input length for the model if that argument is not provided.
-            - `False` or `'do_not_pad'` (default): No padding (i.e., can output a batch with sequences of different
+            - `False` or `'do_not_pad'`: No padding (i.e., can output a batch with sequences of different
               lengths).
         max_length (`int`, *optional*):
             Maximum length of the returned list and optionally padding length (see above).