If you have tested and seen no policy warnings with a newer version (let’s say 3.13 here), you can indicate this with:
cmake_minimum_required(VERSION 2.8...3.13)
This will act like 2.8 as much as possible, but indicates that the project has been tested with 3.13 and does not need to warn about compatibility issues up to that version. It is still recommended to test with your actual minimum version (here, 2.8.0).