Docs: Add @return never to dead_db().

Author: apermo

src/wp-includes/functions.php

@@ -5501,6 +5501,8 @@ function wp_ob_end_flush_all() {
  * @since 2.3.2
  *
  * @global wpdb $wpdb WordPress database abstraction object.
+ *
+ * @return never
  */
 function dead_db() {
 	global $wpdb;