MAINTAINERS: add leah to 6.1 MAINTAINERS file

I've been trying to get backports rolling to 6.1.y. Update MAINTAINERS
file so backports requests / questions can get routed appropriately.

Signed-off-by: Leah Rumancik <leah.rumancik@gmail.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>