[SyncUps] remove @mainactor

Author: meltsplit

Examples/SyncUps/SyncUps/App.swift

@@ -5,7 +5,6 @@ import SwiftUI
 struct SyncUpsApp: App {
   // NB: This is static to avoid interference with Xcode previews, which create this entry
   //     point each time they are run.
-  @MainActor
   static let store = Store(initialState: AppFeature.State()) {
     AppFeature()
       ._printChanges()