buffer: fix 6-byte writeUIntBE() range check

Fixes: https://github.com/nodejs/node/issues/30420

PR-URL: https://github.com/nodejs/node/pull/30459


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>