Use async_refresh() instead of private _refresh()

dask_kubernetes/operator/_objects.py

@@ -71,7 +71,7 @@ async def scheduler_service(self) -> Service:
         return services[0]
 
     async def ready(self) -> bool:
-        await self._refresh()
+        await self.async_refresh()
         return (
             "status" in self.raw
             and "phase" in self.status