Fix: loading DBRX back from saved path (#35728)

* fix dtype as dict for some models + add test

* add comment in tests

tests/test_modeling_common.py

@@ -331,6 +331,12 @@ class ModelTesterMixin:
                 with torch.no_grad():
                     second = model(**self._prepare_for_class(inputs_dict, model_class))[0]
 
+                # Save and load second time because `from_pretrained` adds a bunch of new config fields
+                # so we need to make sure those fields can be loaded back after saving
+                # Simply init as `model(config)` doesn't add those fields
+                model.save_pretrained(tmpdirname)
+                model = model_class.from_pretrained(tmpdirname)
+
             if isinstance(first, tuple) and isinstance(second, tuple):
                 for tensor1, tensor2 in zip(first, second):
                     check_save_load(tensor1, tensor2)