doc: add BethGriggs to collaborators

PR-URL: https://github.com/nodejs/node/pull/19610


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Yuta Hiroto <hello@hiroppy.me>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>