gitlab-ci: Skip ext_timer_query/time-elapsed

This test's result is unpredictable, so it may occasionally pass when we
expect it to fail, thus causing the CI pipeline to fail.

Reviewed-by: Eric Anholt <eric@anholt.net>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3498>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3498>
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 1272d53..cd53f02 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -555,6 +555,7 @@
       -x arb_gpu_shader5
       -x egl_ext_device_
       -x egl_ext_platform_device
+      -x ext_timer_query@time-elapsed
       -x glx-multithread-clearbuffer
       -x glx-multithread-shader-compile
       -x max-texture-size