ci/zink: Enable the validation layer on the TGL GL46 run.

We recently had an issue where an anv merge failed due to a bug in zink,
which validation would have caught.  Get some coverage by default on the
main branch.

This increases runtime from 9:30 to 12:10.  I don't feel good about this,
but I've got https://gitlab.khronos.org/Tracker/vk-gl-cts/-/issues/4398 in
flight to try to knock the time back down.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22459>

.gitlab-ci/common/generate-env.sh

@@ -118,6 +118,7 @@ for var in \
     VK_ICD_FILENAMES \
     VKD3D_PROTON_RESULTS \
     ZINK_DESCRIPTORS \
+    ZINK_DEBUG \
     LVP_POISON_MEMORY \
     ; do
   if [ -n "${!var+x}" ]; then