ci: Disable Xorg's screensaver entirely.

The screensaver kicks in at 10 minutes and obscures the screen,
independent of dpms.  This causes piglit tests to get flaky (swaps start
taking a whole second, and swapbuffersmsc-divisor-zero times out at
exactly the wrong time) and slow if the run takes longer than 10 minutes.

Hopefully with this we'll see some piglit glx flakes go away forever, it
did seem to for this test locally.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11334>

.gitlab-ci/lava/lava.yml.jinja2

@@ -116,7 +116,7 @@ actions:
           # your client's return code
           - "if [ -n $LAVA_START_XORG ]; then
                echo 'touch /xorg-started; sleep 100000' > /xorg-script;
-               env LD_LIBRARY_PATH=/install/lib/ xinit /bin/sh /xorg-script -- /usr/bin/Xorg -noreset -dpms -logfile /Xorg.0.log &
+               env LD_LIBRARY_PATH=/install/lib/ xinit /bin/sh /xorg-script -- /usr/bin/Xorg -noreset -s 0 -dpms -logfile /Xorg.0.log &
                for i in 1 2 3 4 5; do
                  if [ -e /xorg-started ]; then
                    break;