package/php: security bump version to 7.4.18
Changelog: https://www.php.net/ChangeLog-7.php#7.4.18
Release notes: https://www.php.net/releases/7_4_18.php
Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>