lib: fix diagnostics_channel hasSubscribers error

Fixes: https://github.com/nodejs/node/issues/36598

PR-URL: https://github.com/nodejs/node/pull/36599


Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>