fix type hint for SerializationInfo.round_trip (#1576)

Author: davidhewitt

Diff for: python/pydantic_core/core_schema.py

@@ -149,6 +149,7 @@ def exclude_none(self) -> bool: ...
     @property
     def serialize_as_any(self) -> bool: ...
 
+    @property
     def round_trip(self) -> bool: ...
 
     def mode_is_json(self) -> bool: ...