qa.gitlab-ci.yml

This is needed because in `master`, the `gitlab:assets:compile` is
created, but not the `gitlab:assets:compile pull-cache` job, and the
`needs` keyword cannot take jobs that don't exist, thus we have to
create a dedicated job for `master`, with `needs: ["build-qa-image",
"gitlab:assets:compile"]` instead of `needs: ["build-qa-image",
"gitlab:assets:compile pull-cache"]`.

Signed-off-by: Rémy Coutable <remy@rymai.me>