after a rash of positive tests among the cast.In addition, musical guest Charli XCX officially bailed on performing, saying she was “devastated and heartbroken” by the turn of events.Fey’s alleged appearance would mean a return to the 30 Rockefeller Center anchor chair for her: She co-anchored “Weekend Update” alongside Amy Poehler, 50, from 2004 to 2006 and previously with current “Tonight Show” host Jimmy Fallon, 47, from 2000 to 2004.