Apply suggestions from code review

Co-authored-by: compilade <git@compilade.net>

gguf-py/gguf/metadata.py

@@ -115,7 +115,7 @@ class Metadata:
             return {}
 
         with open(model_card_path, "r", encoding="utf-8") as f:
-            return cast("dict[str, Any]", frontmatter.load(f))
+            return frontmatter.load(f).to_dict()
 
     @staticmethod
     def load_hf_parameters(model_path: Optional[Path] = None) -> dict[str, Any]: