[gnome-nibbles/arnaudb/wip/gtk4] Try to fix CI.

[Arnaud B. <arnaudb src gnome org>]

commit 48816560066d1fc8b89caff7403201e0c5b27c83
Author: Arnaud Bonatti <arnaud bonatti gmail com>
Date:   Tue Jun 16 18:35:17 2020 +0200

    Try to fix CI.

 org.gnome.Nibbles.json | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/org.gnome.Nibbles.json b/org.gnome.Nibbles.json
index 124f894..fe3fd03 100644
--- a/org.gnome.Nibbles.json
+++ b/org.gnome.Nibbles.json
@@ -50,6 +50,7 @@
         {
             "name": "libgnome-games-support",
             "buildsystem": "meson",
+            "branch": "arnaudb/wip/gtk4",
             "sources": [
                 {
                     "type": "git",