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/test_users_absent.yml

@@ -1,6 +1,6 @@
 ---
 - name: Include create_users_json.yml
-  import_playbook: create_users_json.yml
+  ansible.builtin.import_playbook: create_users_json.yml
 
 - name: Test users absent
   hosts: ipaserver
@@ -9,11 +9,11 @@
 
   tasks:
   - name: Include users.json
-    include_vars:
+    ansible.builtin.include_vars:
       file: users.json  # noqa 505
 
   - name: Create dict with user names
-    set_fact:
+    ansible.builtin.set_fact:
       user_names: "{{ user_names | default([]) + [{ 'name': item.name }] }}"
     loop: "{{ users }}"