MAINTAINERS: kunit: Add Rae Moar as a reviewer

Rae has been shouldering a lot of the KUnit review burden for the last
year, and will continue to do so in the future. Thanks!

Signed-off-by: David Gow <davidgow@google.com>
Reviewed-by: Rae Moar <rmoar@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>