Update config class check in auto factory (#29854)

src/transformers/models/auto/auto_factory.py

@@ -579,7 +579,7 @@ def register(cls, config_class, model_class, exist_ok=False):
             model_class ([`PreTrainedModel`]):
                 The model to register.
         """
-        if hasattr(model_class, "config_class") and model_class.config_class != config_class:
+        if hasattr(model_class, "config_class") and str(model_class.config_class) != str(config_class):
             raise ValueError(
                 "The model class you are passing has a `config_class` attribute that is not consistent with the "
                 f"config class you passed (model has {model_class.config_class} and you passed {config_class}. Fix "