Fix warnings_checker.dart handling of multitests

tests/language/const_getter_test.dart

 // Copyright (c) 2015, 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.
 
 // Check that const getters are not allowed.
 
 import 'package:expect/expect.dart';
 
 class C {
   const C();
 
-  const /// 01: compile-time error
+  const //# 01: compile-time error
   get x => 1;
 }
 
-const /// 02: compile-time error
+const //# 02: compile-time error
 get y => 2;
 
 main() {
   Expect.equals(1, const C().x);
   Expect.equals(2, y);
 }