Fix warnings_checker.dart handling of multitests

tests/corelib/int_from_environment3_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.
 
 main() {
-  const int.fromEnvironment('NOT_FOUND', defaultValue: ''); // /// 01: compile-time error
-  const int.fromEnvironment('NOT_FOUND', defaultValue: true); // /// 02: compile-time error
-  const int.fromEnvironment(null); // /// 03: compile-time error
-  const int.fromEnvironment(1); // /// 04: compile-time error
-  const int.fromEnvironment([]); // /// 05: compile-time error
+  const int.fromEnvironment('NOT_FOUND', defaultValue: ''); // //# 01: compile-time error
+  const int.fromEnvironment('NOT_FOUND', defaultValue: true); // //# 02: compile-time error
+  const int.fromEnvironment(null); // //# 03: compile-time error
+  const int.fromEnvironment(1); // //# 04: compile-time error
+  const int.fromEnvironment([]); // //# 05: compile-time error
 }