doc: move mafintosh to Collaborators

mafintosh was accidentally added to the TSC list rather than the
Collaborators list. This corrects that.

PR-URL: https://github.com/nodejs/node/pull/19806


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Michaël Zasso <targos@protonmail.com>