Make more code conform to strict null checks (#10219

* Make more code conform to strict null checks

* Fix types

* Fix tests

* Fix remaining test assertions

* Iterate PR

src/toasts/DesktopNotificationsToast.ts

@@ -24,7 +24,7 @@ import { getLocalNotificationAccountDataEventType } from "../utils/notifications
 const onAccept = (): void => {
     Notifier.setEnabled(true);
     const cli = MatrixClientPeg.get();
-    const eventType = getLocalNotificationAccountDataEventType(cli.deviceId);
+    const eventType = getLocalNotificationAccountDataEventType(cli.deviceId!);
     cli.setAccountData(eventType, {
         is_silenced: false,
     });