Fix warnings_checker.dart handling of multitests

tests/compiler/dart2js_extra/type_constant_switch_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 that switching on type literals leads to a compile time error in
 // dart2js since its implementation of [Type] implements 'operator =='.
 
 class C {}
 
 var v;
 
 main() {
   switch (v) {
-    case C: break; // /// 01: compile-time error
+    case C: break; // //# 01: compile-time error
   }
 }