FIX Don't assume model_config contains model_type (#1012)

Author: BenjaminBossan

src/peft/peft_model.py

@@ -673,7 +673,7 @@ def create_or_update_model_card(self, output_dir: str):
         model_config = self.config
         if hasattr(model_config, "to_dict"):
             model_config = model_config.to_dict()
-        if model_config["model_type"] != "custom":
+        if model_config.get("model_type", "custom") != "custom":
             card.data["base_model"] = model_config["_name_or_path"]
 
         lines = card.text.splitlines()