Fix warnings_checker.dart handling of multitests

tests/language/regress_21912_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 21912.
 
 class A {}
 class B extends A {}
 
 typedef T Function2<S, T>(S z);
 typedef B AToB(A x);
 typedef A BToA(B x);
 
 void main() {
   {
     Function2<Function2<A, B>, Function2<B, A>> t1;
     Function2<AToB, BToA> t2;
     Function2<Function2<int, double>, Function2<int, double>> left;
-    left = t1; /// 01: static type warning
-    left = t2; /// 02: static type warning
+    left = t1; //# 01: static type warning
+    left = t2; //# 02: static type warning
   }
 }