[libxml2] Only build GitLab Pages on main repo

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 15111c82c2f58acfd788c80a54624e1598370f17
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Sat Feb 12 21:25:25 2022 +0100

    Only build GitLab Pages on main repo

 .gitlab-ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 73eac104..132bc1f3 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -287,4 +287,4 @@ pages:
       - public/devhelp/Makefile*
       - public/devhelp/*.xsl
   only:
-    - master
+    - master@gitlab-gnome-org/GNOME