Fix warnings_checker.dart handling of multitests

tests/language/string_interpolation6_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.
 
 // A dollar must be followed by a "{" or an identifier.
 
 class StringInterpolation6NegativeTest {
   static testMain() {
     // Dollar not followed by "{" or identifier.
     String regexp;
-    regexp = "^(\\d\\d?)[-/](\\d\\d?)$"; /// 01: compile-time error
+    regexp = "^(\\d\\d?)[-/](\\d\\d?)$"; //# 01: compile-time error
     print(regexp);
   }
 }
 
 main() {
   StringInterpolation6NegativeTest.testMain();
 }