The Indio, California country music festival Stagecoach was initially founded in 2007 as a sister festival to Coachella, and in recent years, it too has become a pressure cooker of celebrity sightings and brand sponsorships. Case in point: Sydney Sweeney's lingerie brand, which is called SYRN but pronounced like "siren" for some reason, had a karaoke bar at Stagecoach, where the Euphoria actor spent her weekend singing with the likes of Diplo, Lance Bass, Ashton Kutcher, and her boyfriend Scooter Braun. There were some country artists there too, though, like Chase Rice, Riley Green, Dan + Shay, and Bailey Zimmerman. Sweeney, who's infamous for her probably-racist American Eagle commercial , and Braun, who's infamous for general music industry sleaziness , were also spotted together at Ella Langley's Friday set.…