Fix a bunch of slow tests (#8634)

* CI should install `sentencepiece`

* Requiring TF

* Fixing some TFDPR bugs

* remove return_dict=False/True hack

Co-authored-by: patrickvonplaten <patrick.v.platen@gmail.com>

tests/test_modeling_tf_electra.py

@@ -249,6 +249,7 @@ class TFElectraModelTest(TFModelTesterMixin, unittest.TestCase):
             self.assertIsNotNone(model)
 
 
+@require_tf
 class TFElectraModelIntegrationTest(unittest.TestCase):
     @slow
     def test_inference_masked_lm(self):