[arch-general] pacsave for nouveau blacklist in nvidia-utils

I've found that when I need to keep nvidia-utils installed whilst still using nouveau (even while using the suggested method in https://wiki.archlinux.org/title/nouveau#Keep_NVIDIA_driver_installed) it gets overridden upon update of nvidia-utils. I believe the way to solve this would be to add a backup section in the PKGBUILD (https://wiki.archlinux.org/title/PKGBUILD#backup)? But I'm not entirely sure. This would be helpful, in my opinion, though, as it would prevent the blacklist from getting invisibly uncommented, and causing problems which may be hard to debug.