Failure to call SavePolicy within the Transaction method when customizing table names

[supuwoerc]

https://github.com/casbin/gorm-adapter/blob/3d3a3c755df913a52c7077694c4b33f175a37894/adapter.go#L719-L725

https://github.com/casbin/gorm-adapter/blob/3d3a3c755df913a52c7077694c4b33f175a37894/adapter.go#L447-L464

https://github.com/casbin/gorm-adapter/blob/3d3a3c755df913a52c7077694c4b33f175a37894/adapter.go#L393-L401

Creating a tx without copying other key information causes truncate table to fail to find the table name。