FIX: Allow staff to view pending/expired invites of other users (PR #14602)

The /u/username/invited.json?filter=expired and /u/username/invited.json?filter=pending APIs are already returning data to admins. However, the can_see_invite_details? boolean was false, which prevented the Ember frontend from showing the tabs correctly. This commit updates the guardian method to match reality.

GitHub

:grin: Can we add a test case here?