Andy Burnham is set to “tinker” with Shabana Mahmood’s immigration reforms in hopes of avoiding a Labour revolt.The Home Secretary kept her job in the transition between Sir Keir Starmer and Mr Burnham, although party sources have claimed the new Prime Minister will water down her reforms to avoid backbench rebellion. Sources have said he is preparing to reduce the proposed length of time some migrants have to wait to gain the right to remain in…