Fix installability on v2022dev2

Demote dependency on ribchester to a suggests since we no longer ship the Canterbury appfw on the Bullseye based v2022dev2.

debian/changelog

+apertis-dev-tools (0.2021.2) apertis; urgency=medium
+
+  * Fix installability on v2022dev2. Demote dependency on ribchester to a
+    suggests since it is not available in v2022dev2.
+
+ -- Emanuele Aina <emanuele.aina@collabora.com>  Mon, 31 May 2021 10:22:03 +0000
+
 apertis-dev-tools (0.2021.1) apertis; urgency=medium
 
   * debian/apertis/gitlab-ci.yml: Drop since we use an external definition