Upgrade/Install: Disable maintenance mode when core auto-update fails.

In [58128], additional maintenance mode calls were added to the automatic updates process. However, there is an early return if a 'core' automatic update fails.

Maintenance mode isn't disabled until later in the `WP_Automatic_Updater::update()` method. This means that maintenance mode may continue to be enabled despite the core update being treated as a skipped update.

This disables maintenance mode before the early return.

Follow-up to [58128].

Props costdev, hellofromTonya, peterwilsoncc.
Fixes #61459. See #58281.

git-svn-id: https://develop.svn.wordpress.org/trunk@58436 602fd350-edb4-49c9-b593-d223f7449a82

Author: costdev

src/wp-admin/includes/class-wp-automatic-updater.php

@@ -511,6 +511,9 @@ public function update( $type, $item ) {
 				&& ( 'up_to_date' === $upgrade_result->get_error_code()
 					|| 'locked' === $upgrade_result->get_error_code() )
 			) {
+				// Allow visitors to browse the site again.
+				$upgrader->maintenance_mode( false );
+
 				/*
 				 * These aren't actual errors, treat it as a skipped-update instead
 				 * to avoid triggering the post-core update failure routines.