What are the "hujjaj" (pilgrimages/arguments) that Shuʿayb stipulated to Moses, eight of which he was to hire him for?

The arguments in Allah Almighty's saying: "That you hire me for eight Hajj" mean years, and the work would be shepherding. And "But if you complete ten, it will be [as a favor] from you" means that the increase beyond the eight years is a voluntary act.