Fix usage of radicale image instead of none

I just noticed that the `none` image was used in place where `radicale` should be used. Fixed in this commit.

setup/flavors/stack/docker-compose.yml

@@ -105,7 +105,7 @@ services:
 
   {% if webdav_enabled %}
   webdav:
-    image: ${DOCKER_ORG:-mailu}/${DOCKER_PREFIX:-}none:${MAILU_VERSION:-{{ version }}}
+    image: ${DOCKER_ORG:-mailu}/${DOCKER_PREFIX:-}radicale:${MAILU_VERSION:-{{ version }}}
     env_file: {{ env }}
     volumes:
       - "{{ root }}/dav:/data"