[gtk/macos-ci] ci: Limit macos runs

[Matthias Clasen <matthiasc src gnome org>]

commit 0336af06f1281a4a294026296bd5b8e7575e11b3
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Jan 6 09:36:02 2021 -0500

    ci: Limit macos runs
    
    We are building the full stack here, which is pretty expensive,
    so only do it for merge requests and master.

 .gitlab-ci.yml | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index c52a26c6c9..5b5ee631a3 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -148,6 +148,9 @@ macos:
   stage: build
   tags:
     - macos
+  only:
+    - master
+    - merge_requests
   needs: []
   before_script:
     - bash .gitlab-ci/show-execution-environment.sh