[SpeechT5HifiGan] Handle batched inputs (#21702)

* [SpeechT5HifiGan] Handle batched inputs

* fix docstring

* rebase and new ruff style

tests/models/speecht5/test_modeling_speecht5.py

@@ -1545,3 +1545,23 @@ class SpeechT5HifiGanTest(ModelTesterMixin, unittest.TestCase):
     # skip because it fails on automapping of SpeechT5HifiGanConfig
     def test_save_load_fast_init_to_base(self):
         pass
+
+    def test_batched_inputs_outputs(self):
+        config, inputs = self.model_tester.prepare_config_and_inputs_for_common()
+
+        for model_class in self.all_model_classes:
+            model = model_class(config)
+            batched_inputs = inputs["spectrogram"].unsqueeze(0).repeat(2, 1, 1)
+
+            batched_outputs = model(batched_inputs)
+            self.assertEqual(
+                batched_inputs.shape[0], batched_outputs.shape[0], msg="Got different batch dims for input and output"
+            )
+
+    def test_unbatched_inputs_outputs(self):
+        config, inputs = self.model_tester.prepare_config_and_inputs_for_common()
+
+        for model_class in self.all_model_classes:
+            model = model_class(config)
+            outputs = model(inputs["spectrogram"])
+            self.assertTrue(outputs.dim() == 1, msg="Got un-batched inputs but batched output")