[Compose] Update Dovecot image

docker-compose.yml

@@ -162,7 +162,7 @@ services:
             - sogo
 
     dovecot-mailcow:
-      image: mailcow/dovecot:1.49
+      image: mailcow/dovecot:1.51
       build: ./data/Dockerfiles/dovecot
       cap_add:
         - NET_BIND_SERVICE