[gnome-shell] ci: Set XDG_RUNTIME_DIR for tests

[Jonas Ådahl <jadahl src gnome org>]

commit da6c154cebcdaf66c92c4c310113573c45e7d60a
Author: Florian Müllner <fmuellner gnome org>
Date:   Sun Aug 25 18:52:49 2019 +0300

    ci: Set XDG_RUNTIME_DIR for tests
    
    Mutter's backend code depends on it being set.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/691

 .gitlab-ci.yml | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index a284b75b7c..cedd587c52 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -67,6 +67,8 @@ build:
 test:
     image: registry.gitlab.gnome.org/gnome/mutter/master:v2
     stage: test
+    variables:
+        XDG_RUNTIME_DIR: "$CI_PROJECT_DIR/runtime-dir"
     before_script:
         - ninja -C mutter/build install
     script: