Notarize in afterSign step instead of afterPack

ts/scripts/after-sign.ts

@@ -0,0 +1,12 @@
+// Copyright 2022 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import type { AfterPackContext } from 'electron-builder';
+import { afterSign as notarize } from './notarize';
+
+// NOTE: It is AfterPackContext here even though it is afterSign.
+// See: https://www.electron.build/configuration/configuration.html#aftersign
+export async function afterSign(context: AfterPackContext): Promise<void> {
+  // This must be the last step
+  await notarize(context);
+}