gitlab-ci: reduce a630 runner load

They seem to be sometimes taking a while to boot, which is triggering CI
timeouts.  (Possibly tftp server in bad shape?)  Cut out non-essential
a630 CI jobs, and reduce the gles3/gles31 jobs to compensate.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5893>
1 file changed