doc: wrap GOVERNANCE.md at 80 characters

This is in preparation for a markdown lint rule requiring lines to be
wrapped at 80 characters.

PR-URL: https://github.com/nodejs/node/pull/24094


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>