[Tests] Add Common Test for Training + Fix a couple of bugs (#8415)

* add training tests

* correct longformer

* fix docs

* fix some tests

* fix some more train tests

* remove ipdb

* fix multiple edge case model training

* fix funnel and prophetnet

* clean gpt models

* undo renaming of albert

src/transformers/modeling_utils.py

@@ -1047,7 +1047,7 @@ class PreTrainedModel(nn.Module, ModuleUtilsMixin, GenerationMixin):
                     f"Some weights of the model checkpoint at {pretrained_model_name_or_path} were not used when "
                     f"initializing {model.__class__.__name__}: {unexpected_keys}\n"
                     f"- This IS expected if you are initializing {model.__class__.__name__} from the checkpoint of a model trained on another task "
-                    f"or with another architecture (e.g. initializing a BertForSequenceClassification model from a BertForPretraining model).\n"
+                    f"or with another architecture (e.g. initializing a BertForSequenceClassification model from a BertForPreTraining model).\n"
                     f"- This IS NOT expected if you are initializing {model.__class__.__name__} from the checkpoint of a model that you expect "
                     f"to be exactly identical (initializing a BertForSequenceClassification model from a BertForSequenceClassification model)."
                 )