Remove a duplicate call to future.set_result when requesting authorization on macOS.

Author: samschott

src/desktop_notifier/backends/macos.py

@@ -175,7 +175,6 @@ async def has_authorisation(self) -> bool:
         def handler(settings: objc_id) -> None:
             settings = py_from_ns(settings)
             future.set_result(settings)
-            future.set_result(settings)
 
         self.nc.getNotificationSettingsWithCompletionHandler(handler)