gitlab-ci: Use virtme-ng for running our tests

virtme-ng is the an update version of virtme, and this patch uses
that instead of the one we had partially modified.

Besides that this partially reverts ad039cdf, 'backend-drm: Enable
atomic async flip support' and makes our CI happier. Specifically
ad039cdf updated our kernel version from 6.3 to 6.9 but did not do
a FDO bum,p and with that, no container images were rebuilt. Effectively
we were still using 6.3.

Now, with the FDO bump, in this patch, we noticed that the drm-writeback
test is failing with linux kernel version 6.9.

So far, only 6.3 and 6.4 kernel versions seems to be working, that is,
without that drm writeback test timing out. The safest bet for the
time being, would be to keep our CI just use 6.3 kernel, until we
have proper version to update to.

Signed-off-by: Daniel Stone <daniel.stone@collabora.com>
Signed-off-by: Marius Vlad <marius.vlad@collabora.com>