tools: update eslint-plugin-markdown configuration

This commit updates the linting setup to work with
eslint-plugin-markdown@2.0.0. This also allows the update-eslint
script to continue to function properly without changes.

PR-URL: https://github.com/nodejs/node/pull/37549


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>