vault: 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/vault/tasks_vault_members.yml

@@ -1,7 +1,7 @@
 ---
   # Tasks to test member management for Vault module.
   - name: Setup testing environment.
-    import_tasks: env_setup.yml
+    ansible.builtin.import_tasks: env_setup.yml
 
   - name: Ensure vault is present
     ipavault:
@@ -315,4 +315,4 @@
     failed_when: result.changed or result.failed
 
   - name: Cleanup testing environment.
-    import_tasks: env_cleanup.yml
+    ansible.builtin.import_tasks: env_cleanup.yml