meta: move pmq20 to Collaborator Emeriti list

Minqi Pan confirmed in email that they were fine with being moved to
Collaborator Emeritus.

PR-URL: https://github.com/nodejs/node/pull/27602


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>