Fix wrong documentation about DataCollator padding defaults (#21919)

* Fix wrong documentation about DataCollator padding defaults

* Fix styling

src/transformers/data/data_collator.py

@@ -274,12 +274,11 @@ class DataCollatorForTokenClassification(DataCollatorMixin):
             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
-              is provided).
+            - `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
-              lengths).
+            - `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).
         pad_to_multiple_of (`int`, *optional*):
@@ -531,12 +530,11 @@ class DataCollatorForSeq2Seq:
             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
-              is provided).
+            - `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
-              lengths).
+            - `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).
         pad_to_multiple_of (`int`, *optional*):