Fix gradient checkpointing + fp16 autocast for most models (#24247)

* fix gc bug

* continue PoC on OPT

* fixes

* 🤯

* fix tests

* remove pytest.mark

* fixup

* forward contrib credits from discussions

* forward contrib credits from discussions

* reverting changes on untouched files.

---------

Co-authored-by: zhaoqf123 <zhaoqf123@users.noreply.github.com>
Co-authored-by: 7eu7d7 <7eu7d7@users.noreply.github.com>

tests/models/autoformer/test_modeling_autoformer.py

@@ -238,6 +238,12 @@ class AutoformerModelTest(ModelTesterMixin, PipelineTesterMixin, unittest.TestCa
     def test_resize_tokens_embeddings(self):
         pass
 
+    @unittest.skip(
+        reason="The model does not support GC + autocast + fp16: https://github.com/huggingface/transformers/pull/24247"
+    )
+    def test_training_gradient_checkpointing_autocast(self):
+        pass
+
     # # Input is 'static_categorical_features' not 'input_ids'
     def test_model_main_input_name(self):
         model_signature = inspect.signature(getattr(AutoformerModel, "forward"))