flake.nix: Improve nixosModules.notDetected error location reporting
flake.nix: Improve nixosModules.notDetected error location reporting

This is mostly equivalent, but `import` was hiding the location
from the module system, breaking error location reporting and
breaking `disabledModules` support for this module (unlikely).

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs