Katy Perry is raising a toast to “The One That Got Away” after her ex, Josh Groban, announced his engagement to British actor Natalie McQueen. The “Firework” singer, 41, shared her reaction to Groban and McQueen’s news in a playful TikTok shared Monday, which started out with just a screenshot of a news story about the engagement. Perry then appeared in a white bathrobe and an exaggerated sad face as she poured a bubbly drink into a glass and raised it in a toast to the happy couple. She then chugged the drink, spilling it on her robe and pretended to sob before walking out of frame. She captioned the post with a simple, “congrats.” The video was soundtracked to her hit 2010 song “The One That Got Away,” which is believed to have been written about musician Groban, 45, after they dated briefly in 2009 and decided to remain friends after their break-up.…