meta: add mailmap entry for KhafraDev

This will make `git log` entries for KhafraDev show up using the name
in the README, which is required so that find-inactive-collaborators.mjs
doesn't incorrectly flag him for removal.

PR-URL: #47512
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Matthew Aitken <maitken033380023@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>

.mailmap

@@ -343,6 +343,7 @@ Matteo Collina <matteo.collina@gmail.com> <hello@matteocollina.com>
 Matthew Lye <muddletoes@hotmail.com>
 Matthew Turner <matty_t47@hotmail.com> <ramesius@users.noreply.github.com>
 Matthias Bastian <dev@matthias-bastian.de> <piepmatz@users.noreply.github.com>
+Matthew Aitken <maitken033380023@gmail.com>
 Maurice Hayward <mauricehayward1@gmail.com>
 Maya Lekova <apokalyptra@gmail.com> <mslekova@chromium.org>
 Mestery <mestery@protonmail.com> <mestery@pm.me>