ci: Revert to a previous version of the flatpak template

A new version seems to be causing some issues, so
use the previous revision until it's resolved

https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1214

.gitlab-ci.yml

@@ -1,4 +1,7 @@
-include: 'https://gitlab.gnome.org/GNOME/citemplates/raw/master/flatpak/flatpak_ci_initiative.yml'
+include:
+  - project: 'gnome/citemplates'
+    ref: '3ecafcc4f06d98a13eb958e86ae0d8c6f388c1aa'
+    file: '/flatpak/flatpak_ci_initiative.yml'
 
 stages:
  - review