Arnetta Johnson, a New Jersey-born trumpeter, was onstage with Beyoncé during the Super Bowl 50 halftime show. But in her last semester at the Berklee College of Music, she had trouble finding other female trumpet players to practice with. “Ultimately it never happened, unfortunately,” Johnson said at the New School on Monday, during a Winter Jazzfest talk called Jazz and Gender: Challenging Inequality and Forging a New Legacy. Percussionist Terri Lyne Carrington was one of Johnson’s professors