Docs: Update the return type for get_current_site()

This is now a `WP_Network` object.

See #32246.


git-svn-id: https://develop.svn.wordpress.org/trunk@36893 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/ms-functions.php

@@ -1590,9 +1590,9 @@ function wpmu_welcome_user_notification( $user_id, $password, $meta = array() )
  *
  * @since MU
  *
- * @global object $current_site
+ * @global WP_Network $current_site
  *
- * @return object
+ * @return WP_Network
  */
 function get_current_site() {
 	global $current_site;