Fix config transaction rendering error on auth page by allowing PhutilSafeHTML
Summary: Closes T15706
Test Plan: Checked that the page worked as expected with changes implemented
Reviewers: O1 Blessed Committers, speck, valerio.bozzolan
Reviewed By: O1 Blessed Committers, speck, valerio.bozzolan
Subscribers: sirocyl, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T15706
Differential Revision: https://we.phorge.it/D25512