[sys.monitoring] Change ignored Callable return type to object (#15217)

stdlib/sys/_monitoring.pyi

@@ -65,4 +65,4 @@ def restart_events() -> None: ...
 DISABLE: Final[object]
 MISSING: Final[object]
 
-def register_callback(tool_id: int, event: int, func: Callable[..., Any] | None, /) -> Callable[..., Any] | None: ...
+def register_callback(tool_id: int, event: int, func: Callable[..., object] | None, /) -> Callable[..., Any] | None: ...