fix(dbus): fix users issues detection (#1317)

Recently, we implemented the Issues API to users management (which was
using the old validation API). However, the manager and the D-Bus
service where using separate `Users` instances.

service/lib/agama/dbus/manager_service.rb

@@ -125,7 +125,7 @@ def manager_dbus
       end
 
       def users_dbus
-        @users_dbus ||= Agama::DBus::Users.new(users, logger)
+        @users_dbus ||= Agama::DBus::Users.new(manager.users, logger)
       end
     end
   end

service/lib/agama/users.rb

@@ -149,7 +149,7 @@ def update_issues
       unless root_password? || root_ssh_key? || first_user?
         new_issues << Issue.new(
           _("Defining a user, setting the root password or a SSH public key is required"),
-          source: Issue::Source::CONFIG,
+          source:   Issue::Source::CONFIG,
           severity: Issue::Severity::ERROR
         )
       end