Update plugin version in sample app (#3005)

Author: buenaflor

flutter/example/pubspec.yaml

@@ -38,7 +38,7 @@ dependencies:
 
 dev_dependencies:
   flutter_lints: ^2.0.0
-  sentry_dart_plugin: ^2.2.0
+  sentry_dart_plugin: ^3.0.0
   integration_test:
     sdk: flutter
   flutter_test: