[gnome-control-center] ci: Prevent stop_review from running on image builds

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

commit 5eef2f4cffef88a422b7140c0dc30a685bcd196e
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Tue Dec 11 11:21:21 2018 -0200

    ci: Prevent stop_review from running on image builds
    
    [skip ci]

 .gitlab-ci.yml | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 00502d7ca..c4e1a0235 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -251,6 +251,9 @@ stop_review:
   environment:
     name: review/$CI_COMMIT_REF_NAME
     action: stop
+  except:
+    variables:
+      - $CI_PIPELINE_SOURCE == "schedule"
 
 # Runs the sanitizers [address, thread, undefined, and memory].
 .sanitizer: &sanitizer