Fix warnings_checker.dart handling of multitests

tests/language/final_param_test.dart

 // Copyright (c) 2011, 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.
 // Disallow assignment of parameters marked as final.
 
 class A {
   static void test(final x) {
-    x = 2; // /// 01: static type warning, runtime error
+    x = 2; // //# 01: static type warning, runtime error
   }
 }
 
 main() {
   A.test(1);
 }