Dart: update dependencies and fixes for latest lints (#6050)

code-samples/community/serving/helloworld-dart/bin/server.dart

@@ -23,7 +23,8 @@ void main(List<String> args) async {
   final ip = InternetAddress.anyIPv4;
 
   // Configure a pipeline that logs requests.
-  final handler = Pipeline().addMiddleware(logRequests()).addHandler(_router);
+  final handler =
+      Pipeline().addMiddleware(logRequests()).addHandler(_router.call);
 
   // For running in containers, we respect the PORT environment variable.
   final port = int.parse(Platform.environment['PORT'] ?? '8080');

code-samples/community/serving/helloworld-dart/pubspec.yaml

@@ -2,7 +2,7 @@ name: hello_world_dart
 publish_to: none # Avoid accidentally publishing this to pub.dev
 
 environment:
-  sdk: ^3.0.0
+  sdk: ^3.1.0
 
 dependencies:
   args: ^2.3.0
@@ -10,6 +10,6 @@ dependencies:
   shelf_router: ^1.1.0
 
 dev_dependencies:
-  http: ^0.13.0
-  lints: ^2.0.0
+  http: ^1.0.0
+  lints: ^4.0.0
   test: ^1.21.0