gitlab-ci: Prune all SCons jobs except scons-win64, and allows failures.

Based on the discussion in https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4352

Reviewed-by: Daniel Stone <daniels@collabora.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4363>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4363>
1 file changed