Correct all @return unknown instances.

See #30224.


git-svn-id: https://develop.svn.wordpress.org/trunk@30202 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/user.php

@@ -195,7 +195,7 @@ function edit_user( $user_id = 0 ) {
  *
  * @since 2.8.0
  *
- * @return unknown
+ * @return array
  */
 function get_editable_roles() {
 	global $wp_roles;