Add skipif for argon2id in test

If argon2i is provided by libargon, then argon2id may not be
available here.

Author: nikic

ext/sodium/tests/bug78516.phpt

@@ -3,6 +3,7 @@ Bug #78516 (password_hash(): Memory cost is not in allowed range)
 --SKIPIF--
 <?php
 if (!extension_loaded('sodium')) die('skip sodium extension not available');
+if (!defined('PASSWORD_ARGON2ID')) die('skip PASSWORD_ARGON2ID not available');
 ?>
 --FILE--
 <?php