By Daniel Chavkin Miami has endured six losing seasons since Mattingly took over as manager. After the MLB season ends, the Marlins will have a new manager. Marlins insider Craig Mish reports Miami and manager Don Mattingly have “mutually agreed” that Mattingly will not manage the team after this year. After five winning seasons as the Dodgers manager, Mattingly took over the Marlins in 2016 and is by far the winningest manager in franchise history with 437 wins. His seven years as manager is three more than any other manager in team history. In those seven seasons with Mattingly at the helm, …