panfrost/ci: Skip draw_buffers_indexed.random.* on Midgard

panfrost/ci: Skip draw_buffers_indexed.random.* on Midgard

These are (have always been) quite broken. Given that the whole section is
already in the flakes.txt, and there's no plan for improving this (I've tried
and fails), I'd rather just skip the section and reduce the noise in
the #panfrost-ci channel.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Reviewed-by: Emma Anholt <emma@anholt.net>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21891>