Dont show token notification when sign in sheet open

Summary: This is an edge case where if we make a intern call  to fetch user with an invalid token we would imply that the token may have expired. Since we already have a error message in the sign in sheet we dont show the notification

Reviewed By: aigoncharov

Differential Revision: D44502480

fbshipit-source-id: 531df6db28bc2a6f36ffcf0a3903ee0e8e40be0f

desktop/flipper-ui-core/src/chrome/fb-stubs/SignInSheet.tsx

@@ -7,6 +7,10 @@
  * @format
  */
 
+export function isSheetOpen(): boolean {
+  return false;
+}
+
 export async function showLoginDialog(
   _initialToken: string = '',
 ): Promise<boolean> {