[librsvg] Run the "make distcheck" CI only on schedule

[Federico Mena Quintero <federico src gnome org>]

commit 0f833ca8b97584c705ed97fa8e97639c89815a43
Author: Federico Mena Quintero <federico gnome org>
Date:   Tue Oct 29 20:39:18 2019 -0600

    Run the "make distcheck" CI only on schedule
    
    Hmmm, it takes less time than "make check"?

 .gitlab-ci.yml | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 45ca6e55..11be28f9 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -187,6 +187,7 @@ tarball:
   script:
     - cd _build
     - make distcheck DESTDIR=/tmp/distcheck
+  <<: *stage_3
 
 # STAGE 3 CROSS DISTRO TESTS
 #######################################################################