MAINTAINERS: exec: Mark Kees as maintainer

It's more accurate to mark myself as a maintainer: I've been keeping the
tree up to date in linux-next, etc.

Link: https://lore.kernel.org/r/20241031220853.work.354-kees@kernel.org


Reviewed-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Kees Cook <kees@kernel.org>