[gtk/gtk3-debian-ci: 1/2] ci: Update Debian image to current stable

[Emmanuele Bassi <ebassi src gnome org>]

commit 7e2917e19caedd64a58cee4a206b4749f21e4670
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Mon Oct 4 13:23:32 2021 +0100

    ci: Update Debian image to current stable
    
    This is required by a change in the certificates that makes it
    impossible to run `git clone` on a GNOME GitLab repository in a CI
    pipeline.

 .gitlab-ci/debian-gtk3.Dockerfile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab-ci/debian-gtk3.Dockerfile b/.gitlab-ci/debian-gtk3.Dockerfile
index d8007a731a..469be4f5a2 100644
--- a/.gitlab-ci/debian-gtk3.Dockerfile
+++ b/.gitlab-ci/debian-gtk3.Dockerfile
@@ -1,4 +1,4 @@
-FROM debian:buster
+FROM debian:bullseye
 
 RUN apt-get update -qq && apt-get install --no-install-recommends -qq -y \
     adwaita-icon-theme \