Add `@see` reference for `set_post_thumbnail()` in the phpDoc for `wp_ajax_set_attachment_thumbnail()`.

See #27891.

Built from https://develop.svn.wordpress.org/trunk@29037


git-svn-id: http://core.svn.wordpress.org/trunk@28825 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/ajax-actions.php

@@ -1950,6 +1950,8 @@ function wp_ajax_set_post_thumbnail() {
  * Ajax handler for setting the featured image for an attachment.
  *
  * @since 4.0.0
+ *
+ * @see set_post_thumbnail()
  */
 function wp_ajax_set_attachment_thumbnail() {
 	if ( empty( $_POST['urls'] ) || ! is_array( $_POST['urls'] ) ) {