fix: move child to right widget in dependency injection page (flutter…

…#11529)

src/content/app-architecture/case-study/dependency-injection.md

@@ -92,8 +92,8 @@ runApp(
       ),
       // In the Compass app, additional service and repository providers live here.
     ],
+    child: const MainApp(),
   ),
-  child: const MainApp(),
 );
 ```