[server] Prevent updateThread from converting to PERSONAL/PRIVATE outside scripts

Summary: Updating this condition to handle PRIVATE thread and excluding scripts (since we're about to call it from a script)

Test Plan: Flow

Reviewers: subnub, palys-swm

Reviewed By: palys-swm

Subscribers: KatPo, zrebcu411, Adrian, atul, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D787