Add assertion to _CupertinoSwitchRenderObjectWidget, otherwise it is confusing...

Add assertion to _CupertinoSwitchRenderObjectWidget, otherwise it is confusing why updateRenderObject omits state update (#112044)

packages/flutter/lib/src/cupertino/switch.dart

@@ -378,6 +378,7 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
 
   @override
   void updateRenderObject(BuildContext context, _RenderCupertinoSwitch renderObject) {
+    assert(renderObject._state == state);
     renderObject
       ..value = value
       ..activeColor = activeColor