Broadcast cluster's disconnected state before stopping KubeAuthProxy (#4273)

src/main/catalog-sources/__test__/kubeconfig-sync.test.ts

@@ -42,6 +42,7 @@ jest.mock("electron", () => ({
   },
   ipcMain: {
     on: jest.fn(),
+    once: jest.fn(),
     handle: jest.fn(),
   },
 }));