[constellation] Pin Django from Debian experimental until bullseye-backports got released

Signed-off-by: Yohann D'ANELLO <ynerant@crans.org>

roles/constellation/tasks/main.yml

 ---
+- name: Pin Django from Debian experimental until bullseye-backports exists
+  template:
+    src: "apt/{{ item }}.j2"
+    dest: "/etc/apt/{{ item }}"
+  loop:
+    - sources.list.d/experimental.list
+    - preferences.d/django-experimental
+
 - name: Install constellation dependencies
   apt:
     update_cache: true

roles/constellation/templates/apt/preferences.d/django-experimental.j2

+{{ ansible_header | comment }}
+
+
+Package: *
+Pin: release n=experimental
+Pin-Priority: 1
+
+
+Package: python3-django
+Pin: release n=experimental
+Pin-Priority: 900
+
+
+Package: python3-django-tables2
+Pin: release n=experimental
+Pin-Priority: 900

roles/constellation/templates/apt/sources.list.d/experimental.list.j2

+{{ ansible_header | comment }}
+
+deb {{ debian_mirror }} experimental main