Katy Perry and John Mayer had a double date on Grammy night with “Girls” actress Allison Williams and her reported boyfriend, College Humor founder Ricky Van Veen. The foursome was spotted arriving at André Balazs’ Chateau Marmont for Warner Music Group’s awards party Sunday, and settling into a corner booth while “Girls” creator Lena Dunham held court with her Grammy-winning boyfriend Jack Antonoff at another table. Sting and Trudie Styler arrived early and sat with guests including Neil Patrick Harris and David Burtka, Alessandra Ambrosio and Selena Gomez (who was overheard earlier complaining that her ex Justin Bieber “is always texting her.”) Santigold