chore(kube): bump stalwartlabs/stalwart Docker tag to v0.16.21

docker/infrastructure/mail/roundcube/docker-compose.yml

@@ -1,6 +1,6 @@
 services:
   roundcube:
-    image: roundcube/roundcubemail:1.7.4-apache
+    image: roundcube/roundcubemail:1.7.2-apache
     container_name: roundcube
     networks:
       - default

kubernetes/infrastructure/mail/stalwart/values.yaml

@@ -7,7 +7,7 @@
 # Container image
 image:
     repository: stalwartlabs/stalwart
-    tag: v0.16.20
+    tag: v0.16.21
     pullPolicy: IfNotPresent
 # Single-node RocksDB deployment.
 replicaCount: 1