ansible.cfg: Use new callbacks_enabled key name

As per the following deprecation warning (even though it has a typo):

[DEPRECATION WARNING]: [defaults]callback_whitelist option, normalizing
names to new standard, use callback_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.

[1] https://github.com/ansible/ansible/pull/74845