Crash in setUserId in iOS 18

[andy-vanwagoner-jn]

stack trace in organizer

It looks like the dictionary PushNotifications.shared.tokenProvider or serverSyncEventHandler.userIdCallbacks is being accessed concurrently on different threads, which causes the crash. I haven't been able to reproduce the issue locally, but I have 1,864 devices affected in organizer in the last 2 weeks.

I'll try to consistently call on a particular thread to see if that helps.