[skip ci] Mark new firebird tests with xleak

Author: iluuu1994

ext/pdo_firebird/tests/pdofirebird_001.phpt

@@ -4,6 +4,9 @@ PDO_firebird subclass basic
 pdo_firebird
 --SKIPIF--
 <?php require(__DIR__ . '/skipif.inc'); ?>
+--XLEAK--
+A bug in firebird causes a memory leak when calling `isc_attach_database()`.
+See https://github.com/FirebirdSQL/firebird/issues/7849
 --FILE--
 <?php
 

ext/pdo_firebird/tests/pdofirebird_002.phpt

@@ -4,6 +4,9 @@ PDO_firebird connect through PDO::connect
 pdo_firebird
 --SKIPIF--
 <?php require(__DIR__ . '/skipif.inc'); ?>
+--XLEAK--
+A bug in firebird causes a memory leak when calling `isc_attach_database()`.
+See https://github.com/FirebirdSQL/firebird/issues/7849
 --FILE--
 <?php