[gnome-control-center] CI: run coverage only on master

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 94ba4c89dae79a2dd893c6e2e2674787e2b890c7
Author: Claudio André <claudioandre br gmail com>
Date:   Sun Jul 15 11:22:30 2018 -0300

    CI: run coverage only on master
    
    To save resources. It is unlikely that anyone would want this information
    from a branch. If necessary, we must create a manual job.

 .gitlab-ci.yml | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 77ddf5f6c..ee7706d5b 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -90,6 +90,8 @@ coverage:
   variables:
     BUILD_OPTS: "-Db_coverage=true"
     coverage: '/^Lines:.\d+.\d+.(\d+\.\d+\%)/'
+  only:
+    - master@GNOME/gnome-control-center
 
   script:
     - *environment_information