Examples: use const modifier for MyApp.

Author: greenrobot-team

objectbox/example/flutter/objectbox_demo/lib/main.dart

@@ -17,7 +17,7 @@ Future<void> main() async {
 
   objectbox = await ObjectBox.create();
 
-  runApp(MyApp());
+  runApp(const MyApp());
 }
 
 class MyApp extends StatelessWidget {

objectbox/example/flutter/objectbox_demo_sync/lib/main.dart

@@ -17,7 +17,7 @@ Future<void> main() async {
 
   objectbox = await ObjectBox.create();
 
-  runApp(MyApp());
+  runApp(const MyApp());
 }
 
 class MyApp extends StatelessWidget {