doc: fix `events.getEventListeners` example

PR-URL: https://github.com/nodejs/node/pull/36085


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>