automation: Update watchtower Docker tag to v1.5.1

roles/docker_watchtower/defaults/main.yml

@@ -27,7 +27,7 @@ watchtower_registry_auths: {}
 #watchtower_notifications_shoutrrr_hook: 'https://....'
 
 # renovate: depName=docker.io/containrrr/watchtower
-watchtower_version: 1.4.0
+watchtower_version: 1.5.1
 # renovate: depName=quay.io/sheogorath/docker-socket-proxy
 watchtower_dockersocket_version: "2.3"