load_state_dict is a method, which should get the state_dict as its input.
Currently you are reassigning the state_dict to the function:
self.model.load_state_dict = checkpoint['state_dict']
self.optimizer.load_state_dict = checkpoint['optimizer']

Replace these lines of code with:
self.model.load_state_dict(checkpoint['state_dict'])
self.optimizer.load_state_dict(checkpoint['optimizer'])

and rerun the code.