Signal a “Firework” — Katy Perry just announced her final season at American Idol! The pop star revealed the upcoming season of the singing competition series will likely be her last, as she looks to start the next chapter of her life roughly six years after her start on the show during its ABC revival in 2018. Perry — who has been engaged to Orlando Bloom since February 2019 — announced the news during a guest appearance on Jimmy Kimmel Live! on Monday night, February 12. “I think this probably will be my last show, my last season for Idol,” the “Dark Horse” singer surprisingly declared to ho…