Fix dt proj bias reassigned (#33314)
* When we set self.dt_proj.bias = None, it removes the bias parameter from the model. When we later tried to assign a tensor to self.dt_proj.bias, it caused a TypeError because PyTorch expects a Parameter object.
* When we set self.dt_proj.bias = None, it removes the bias parameter from the model. When we later tried to assign a tensor to self.dt_proj.bias, it caused a TypeError because PyTorch expects a Parameter object.
* When we set self.dt_proj.bias = None, it removes the bias parameter from the model. When we later tried to assign a tensor to self.dt_proj.bias, it caused a TypeError because PyTorch expects a Parameter object.