ci: bring back the valve farm

Valve infra is back online, sorry for the noise!

This is a partial revert of commit 628d21c521.

Signed-off-by: Martin Roukala (né Peres) <martin.roukala@mupuf.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23571>

.gitlab-ci.yml

@@ -36,7 +36,7 @@ variables:
   LIMA_FARM: "online"
   IGALIA_FARM: "online"
   ANHOLT_FARM: "online"
-  VALVE_FARM: "offline"
+  VALVE_FARM: "online"
   AUSTRIANCODER_FARM: "online"  # only etnaviv GPUs
 
 default: