Since the shebang calls nix-shell, we can safely assume that Nix (Lix,
C++ Nix) is installed. Our scripts should support a wide enough range of
Nix versions so that using the “impure” version of the tool is not a
problem.
This works around #400784. My theory is that the Nix frontend commands
no longer work with older versions of the Nix daemon nor the Lix daemon
in our workloads.
c85656eae6