macos: Take in automatic override of applicationSupportsSecureRestora…

…bleState

This change was made automatically by `flutter run`,
along with the following warning:

  macos/Runner/AppDelegate.swift does not override
    applicationSupportsSecureRestorableState. Updating.

See upstream commit that introduced this override:
  flutter/flutter@68f375f

macos/Runner/AppDelegate.swift

@@ -6,4 +6,8 @@ class AppDelegate: FlutterAppDelegate {
   override func applicationShouldTerminateAfterLastWindowClosed(_ sender: NSApplication) -> Bool {
     return true
   }
+
+  override func applicationSupportsSecureRestorableState(_ app: NSApplication) -> Bool {
+    return true
+  }
 }