Improve arc-browse for php 8.1

Summary: Ref T15064.

Test Plan: ran some arc browse commands in php 8.1, got no exceptions.

Reviewers: O1 Blessed Committers, valerio.bozzolan, Sten

Reviewed By: O1 Blessed Committers, valerio.bozzolan, Sten

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

Maniphest Tasks: T15064

Differential Revision: https://we.phorge.it/D25339