Fix warnings_checker.dart handling of multitests

tests/language/dynamic2_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 //
 // Test the prohibited use of 'dynamic' in extending and implementing classes.
 
 class A
-  extends dynamic // /// 00: compile-time error
-  implements dynamic // /// 01: compile-time error
+  extends dynamic // //# 00: compile-time error
+  implements dynamic // //# 01: compile-time error
 {
 }
 
 main() {
   new A();
 }