doc: move gibfahn to emeritus

Asked Gibson in email if he should be moved to emeritus and he indicated
it was a good idea.

PR-URL: https://github.com/nodejs/node/pull/34190


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>