ci: Run dconf update before running tests

Otherwise tests will fail due to the following warning:

(mutter-test-runner:3700): dconf-WARNING **: 06:39:42.124: unable to
open file '/etc/dconf/db/local': Failed to open file
“/etc/dconf/db/local”: open() failed: No such file or directory; expect
degraded performance

https://gitlab.gnome.org/GNOME/mutter/merge_requests/591

.gitlab-ci.yml

@@ -38,6 +38,7 @@ test-mutter:
     MALLOC_CHECK_: "3"
     NO_AT_BRIDGE: "1"
   script:
+    - dconf update
     - mkdir -m 700 $XDG_RUNTIME_DIR
     - glib-compile-schemas $GSETTINGS_SCHEMA_DIR
     - >