[generation] bring back tests on vision models (#38603)

* bring back geenration tests on VLMs

* remove head mask tests overwritten

tests/models/speecht5/test_modeling_speecht5.py

@@ -741,10 +741,6 @@ class SpeechT5ForSpeechToTextTest(ModelTesterMixin, unittest.TestCase, Generatio
         if hasattr(module, "masked_spec_embed") and module.masked_spec_embed is not None:
             module.masked_spec_embed.data.fill_(3)
 
-    @unittest.skip(reason="Temporarily broken")  # TODO (joao, eustache): have a look at this test
-    def test_generate_with_head_masking(self):
-        pass
-
     @unittest.skip(reason="Temporarily broken")  # TODO (joao, eustache): have a look at this test
     def test_generate_without_input_ids(self):
         pass