fix: remove warning when using 'append' without 'groups'

tasks/create_users.yml

@@ -13,7 +13,7 @@
     uid: "{{ item.uid }}"
     group: "{{ item.primary_group }}"
     groups: "{{ item.groups | default(omit) }}"
-    append: true
+    append: "{{ true if item.groups is defined else false }}"
     create_home: "{{ item.create_home }}"
     home: "{{ item.home }}"
     password: "{{ item.password }}"