[meld] CI: Pin our CI SDK version

[Kai Willadsen <kaiw src gnome org>]

commit 1b50df56a2d7e80111845129386c7019e317a2fc
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Sun Jul 10 09:20:27 2022 +1000

    CI: Pin our CI SDK version
    
    This is an attempt to fix current CI breakage, possibly caused by an
    update to use the 22.08 beta freedesktop base.

 .gitlab-ci.yml | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index f65d6568..c78ccc96 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,6 +1,9 @@
 include: 'https://gitlab.gnome.org/GNOME/citemplates/raw/master/flatpak/flatpak_ci_initiative.yml'
 
-image: registry.gitlab.gnome.org/gnome/gnome-runtime-images/gnome:master
+variables:
+  GNOME_SDK: 42
+
+image: registry.gitlab.gnome.org/gnome/gnome-runtime-images/gnome:${GNOME_SDK}"
 
 stages:
   - check