gitlab-ci: Only pull/push cache contents in build+test stage jobs

The containers-build stage job doesn't use the cache, so this might save
some wasted time for it.

Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>

.gitlab-ci.yml

@@ -20,10 +20,6 @@ variables:
   UBUNTU_IMAGE: "$CI_REGISTRY_IMAGE/ubuntu:$UBUNTU_TAG"
   UBUNTU_IMAGE_MAIN: "registry.freedesktop.org/mesa/mesa/ubuntu:$UBUNTU_TAG"
 
-cache:
-  paths:
-    - ccache
-
 stages:
   - containers-build
   - build+test
@@ -69,6 +65,9 @@ ubuntu:
   extends: .ci-run-policy
   image: $UBUNTU_IMAGE
   stage: build+test
+  cache:
+    paths:
+      - ccache
   artifacts:
     when: on_failure
     untracked: true