[generate] return Cache object even if passed in a legacy format (#35673)

* generate returns a Cache object by default

* fix tests

* fix test for encoder-decoder models

tests/models/jetmoe/test_modeling_jetmoe.py

@@ -18,7 +18,6 @@ import gc
 import unittest
 
 import pytest
-from parameterized import parameterized
 
 from transformers import AutoTokenizer, JetMoeConfig, is_torch_available
 from transformers.testing_utils import (
@@ -299,10 +298,6 @@ class JetMoeModelTest(ModelTesterMixin, GenerationTesterMixin, PipelineTesterMix
     test_disk_offload_bin = False
     test_disk_offload_safetensors = False
 
-    @parameterized.expand([(1, False), (1, True), (4, False)])
-    def test_new_cache_format(self, num_beams, do_sample):
-        pass
-
     def setUp(self):
         self.model_tester = JetMoeModelTester(self)
         self.config_tester = ConfigTester(