title: Environment size class not updated
body: <p>I want to create different layouts using size classes and I followed this example: <a href="https://www.hackingwithswift.com/quick-start/swiftui/how-to-create-different-layouts-using-size-classes" rel="nofollow noreferrer">https://www.hackingwithswift.com/quick-start/swiftui/how-to-create-different-layouts-using-size-classes</a></p>
  
  <p>I extended the Xcode Master/Detail template and changed the ContentView as follows, with the two size classes and then using the horizontal size class to set a size class dependent navigation title. <strong>The problem is the navigation title would always read as "Compact".</strong> What am I missing here?</p>
  
  <pre><code>struct ContentView: View {
      @Environment(\.managedObjectContext)
      var viewContext   
  
      @Environment(\.verticalSizeClass) var vSizeClass
      @Environment(\.horizontalSizeClass) var hSizeClass
  
      var body: some View {
          NavigationView {
              MasterView()
                  .navigationBarTitle(Text(hSizeClass == .compact ? "Compact" : "Regular"))
                  .navigationBarItems(
                      leading: EditButton(),
                      trailing: Button(
                          action: {
                              withAnimation { Event.create(in: self.viewContext) }
                          }
                      ) { 
                          Image(systemName: "plus")
                      }
                  )
              Text("Detail view content goes here")
                  .navigationBarTitle(Text("Detail"))
          }.navigationViewStyle(DoubleColumnNavigationViewStyle())
      }
  }
  </code></pre>