When running molecule jobs, we saw the folloing warning message:

 [DEPRECATION WARNING]: [defaults]callback_whitelist option, normalizing names
 to new standard, use callbacks_enabled instead. This feature will be removed
 from ansible-core in version 2.15. Deprecation warnings can be disabled by
 setting deprecation_warnings=False in ansible.cfg.

callbacks_enabled has been added since Ansible 2.11 and Kubespray is using
Ansible 2.12 at master branch. So we can use callbacks_enabled safely to
avoid the warning message.