doc: fix description of hasSubscribers

PR-URL: https://github.com/nodejs/node/pull/37324


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Harshitha K P <harshitha014@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>