Fix warnings_checker.dart handling of multitests

tests/language_strong/final_is_not_const_test.dart

 // Copyright (c) 2012, 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.
 
 import "package:expect/expect.dart";
 
 final F0 = 42;
-const C0 = F0; // /// 01: compile-time error
+const C0 = F0; // //# 01: compile-time error
 
 main() {
   Expect.equals(42, F0);
-  Expect.equals(42, C0); // /// 01: continued
+  Expect.equals(42, C0); // //# 01: continued
 }