fix CI for users with no installer-test cachix
fix CI for users with no installer-test cachix

Closes #5173

NixOS/nix,NixOS/nix,rycee/nix,rycee/nix,rycee/nix,NixOS/nix,NixOS/nix,NixOS/nix,rycee/nix,rycee/nix