Another solution for anyone encountering this and wanting to prevent the warnings: disable this repository except when you are actively using it. Given that the binary files are unlikely to ever change again, there really is no need to regularly check for updates after setting up working drivers, except possibly around the major updates of your Linux distro. For context, there has not been an update to most driver packages in over 4 years, and it is entirely possible that there will never be another major change to most of them.