Fix "Register with Approval flow" for php 8

Summary: Ref T15064.

Test Plan:
- Register as a new user
- as admin, view user's page and approve it
- As new user, hit "wait patiently" to go back to Home

No crashes in this flow.

Reviewers: O1 Blessed Committers, chris

Reviewed By: O1 Blessed Committers, chris

Subscribers: speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15064

Differential Revision: https://we.phorge.it/D25317