Update paid time off to mention Australian entity

Why is this change being made?

When reviweing the update to the manager role with regard to PTOs, I could not find mention of Australia.

This MR rewords the "New Zealand" entity to GitLab PTY (Australia & New Zealand) , matching what's used in https://about.gitlab.com/handbook/total-rewards/benefits/general-and-entity-benefits/#entity-benefits

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