[Bug]: building with nix broke

### Bug summary nix build \ --extra-substituters "https://nix-wpe-webkit.cachix.org" \ --extra-trusted-public-keys "nix-wpe-webkit.cachix.org-1:ItCjHkz1Y5QcwqI9cTGNWHzcox4EqcXqKvOygxpwYHE=" results in "error: flake 'git+file:///home/arthur/src/neomacs' does not provide attribute 'packages.x86_64-linux.default' or 'defaultPackage.x86_64-linux'" ### Steps to reproduce _No response_ ### Expected behavior _No response_ ### Runtime diagnostics ```shell ``` ### Extra context _No response_