[gnome-control-center] ci: Correctly update the submodules on build.

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 3cad3aaf4158a92e0881d201df4fb6e8dde164c0
Author: Robert Ancell <robert ancell canonical com>
Date:   Fri Sep 25 14:47:20 2020 +1200

    ci: Correctly update the submodules on build.

 .gitlab-ci.yml | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 92de7d944..d3d2e236a 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -58,6 +58,7 @@ variables:
     xorg-x11-server-Xvfb
     mesa-dri-drivers
     libsecret-devel
+  GIT_SUBMODULE_STRATEGY: normal
 
 image: "$FEDORA_IMAGE"