Fix warnings_checker.dart handling of multitests

tests/language_strong/regress_22976_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.
 
 // Regression test for issue 22976.
 
 class A<T> {}
 class B<T> implements A<T> {}
 class C<S, T> implements B<S>, A<T> {}
 
 main() {
-  A<int> a0 = new C<int, String>(); /// 01: ok
-  A<int> a1 = new C<String, int>(); /// 02: ok
+  A<int> a0 = new C<int, String>(); //# 01: ok
+  A<int> a1 = new C<String, int>(); //# 02: ok
 }