update code snippets

Author: buenaflor

docs/platforms/dart/index.mdx

@@ -68,7 +68,7 @@ Verify that your app is sending events to Sentry by adding the following snippet
 import 'package:sentry/sentry.dart';
 
 try {
-  aMethodThatMightFail();
+  throw Exception('Sentry Test Error');
 } catch (exception, stackTrace) {
   await Sentry.captureException(
     exception,