ci: introduce artefacts section for piglit-gl

Missed with earlier commit.

Fixes: c203776 ("ci: split the cts jobs in two")
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Elie Tournier <elie.tournier@collabora.com>

ci/.gitlab-ci.yml

@@ -106,6 +106,11 @@ piglit - gl host:
     - merge_requests
     - schedules
 
+  artifacts:
+    when: always
+    paths:
+      - results/
+
 piglit - gles host:
   stage: test
   services: