Menus: Add item_updated label for wp_navigation post type.

This ensures the appropriate "Navigation Menu updated." message is shown in the snackbar after updating a navigation menu in the Site Editor. Without this, a generic "Post updated." message is displayed.

Developed in WordPress#10882

Follow-up to [58055], [52145], [52069].

Props juanfra.
See #61095.
Fixes #64611.


git-svn-id: https://develop.svn.wordpress.org/trunk@61596 602fd350-edb4-49c9-b593-d223f7449a82

Author: westonruter

src/wp-includes/post.php

@@ -559,6 +559,7 @@ function create_initial_post_types() {
 				'filter_items_list'     => __( 'Filter Navigation Menu list' ),
 				'items_list_navigation' => __( 'Navigation Menus list navigation' ),
 				'items_list'            => __( 'Navigation Menus list' ),
+				'item_updated'          => __( 'Navigation Menu updated.' ),
 			),
 			'description'           => __( 'Navigation menus that can be inserted into your site.' ),
 			'public'                => false,