“This is so dumb. Ten years later. How is this even a story? This is so stupid.” — Victoria Justice is speaking out against the long-running rumor that she was “jealous” of her former Victorious costar Ariana Grande. Victoria, 30, and Ariana, 29, portrayed high schoolers Tori Vega and Cat Valentine on the hit Nickelodeon series from 2010 to 2013, alongside Liz Gillies, Avan Jogia, Daniella Monet, Leon…