Skip gh20122.phpt on pdo_mysql + libmysqlclient

FIELD_TYPE_JSON is a mysqlnd only feature.

Author: iluuu1994

ext/pdo_mysql/tests/gh20122.phpt

@@ -8,6 +8,7 @@ pdo_mysql
 require __DIR__ . '/config.inc';
 require __DIR__ . '/../../../ext/pdo/tests/pdo_test.inc';
 PDOTest::skip();
+if (!MySQLPDOTest::isPDOMySQLnd()) die('skip only for mysqlnd');
 ?>
 --FILE--
 <?php