Glen Tetley's fantastical ballet, set to an atonal Schoenberg score, is finally returning to Covent Garden. Dancers Marcelino Sambé and Joshua Junker discuss how they came under its spell Marcelino Sambé is hanging upside down from a scaffold tower. "It's scary," he tells me. Nevertheless he swings, he swoons, he balances with limbs entwined around the narrow bars, reaching up to an imagined starry sky (it's actual…