run delete as background task, fixes #4339

Author: rodja

nicegui/persistence/redis_persistent_dict.py

@@ -63,4 +63,4 @@ async def close(self) -> None:
 
     def clear(self) -> None:
         super().clear()
-        self.redis_client.delete(self.key)
+        background_tasks.create(self.redis_client.delete(self.key), name=f'redis-delete-{self.key}')