user: Use FQCN for ansible.builtin

Use Fully Qualified Collection Name (FQCN) for ansible builtins. This is
ansible.builtin.set_fact instead of set_fact for example and aplies for
all actions that are part of ansible.builtin.

All the replaced ansible.builtins:
  assert, command, copy, debug, fail, fetch, file, import_playbook,
  import_tasks, include_role, include_tasks, include_vars, package,
  set_fact, shell, slurp, stat, systemd

tests/user/create_users_json.yml

@@ -4,10 +4,10 @@
 
   tasks:
   - name: Check if users.json exists
-    stat:
+    ansible.builtin.stat:
       path: users.json
     register: register_stat_users
 
   - name: Create users.json
-    command: /bin/bash users.sh 500
+    ansible.builtin.command: /bin/bash users.sh 500
     when: not register_stat_users.stat.exists