Starting in Catalina, macOS runs a syspolicyd "assessment" that hits the network for each binary/script executable. It does cache these results, but Nix tends to introduce many "new" executables per build. (You can read more about this at https://github.com/NixOS/nix/issues/3789).
This PR adds a temporary, redundant macOS job with these assessments disabled. I'm hoping you can adopt it for a few weeks to help me collect more data on how this affects real projects.
Following discussion with Shea and Graham. It's a big enough change
from the last release. Also, from a semver perspective, 2.0 makes more
sense because we did remove some interfaces (like nix-pull/nix-push).
