doc: fix bugs in _construct() example

PR-URL: https://github.com/nodejs/node/pull/36509


Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>