[T5] Adding `model_parallel = False` to `T5ForTokenClassification` and...

[T5] Adding `model_parallel = False` to `T5ForTokenClassification` and `MT5ForTokenClassification` (#30763)

* Adding model_parallel = False

* Revert "Adding model_parallel = False"

This reverts commit ba1d99976acb598824ce3347dbe7d848daa21e79.

* Trainer: circumvent error for model  in which is_parallelizable is True but does not have model_parallel attribute

src/transformers/trainer.py

@@ -436,7 +436,7 @@ class Trainer:
                 "https://huggingface.co/docs/transformers/model_doc/auto"
             )
 
-        if hasattr(model, "is_parallelizable") and model.is_parallelizable and model.model_parallel:
+        if getattr(model, "is_parallelizable", False) and getattr(model, "model_parallel", False):
             self.is_model_parallel = True
         else:
             self.is_model_parallel = False