Cron API: Use WEEK_IN_SECONDS constant for the weekly schedule added in [47062].

Props afercia.
See #47606.

git-svn-id: https://develop.svn.wordpress.org/trunk@47068 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/cron.php

@@ -825,7 +825,7 @@ function wp_get_schedules() {
 			'display'  => __( 'Once Daily' ),
 		),
 		'weekly'     => array(
-			'interval' => 7 * DAY_IN_SECONDS,
+			'interval' => WEEK_IN_SECONDS,
 			'display'  => __( 'Once Weekly' ),
 		),
 	);