[gdk-pixbuf/macos-ci] ci: Limit macOS builds

[Emmanuele Bassi <ebassi src gnome org>]

commit 048938a62a9612ac6ad860ad55e554aec69a1fff
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Mon Jan 4 00:49:57 2021 +0000

    ci: Limit macOS builds
    
    Only build on macOS for merge requests and the main development branch.

 .gitlab-ci.yml | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 08d3ca080..ec1d34663 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -56,6 +56,9 @@ meson-fedora-x86_64:
 macos:
   stage: build
   needs: []
+  only:
+    - master
+    - merge_requests
   tags:
     - macos
   before_script: