feat: add unstable nixpkgs overlay

hosts/gwiad/configuration.nix

@@ -2,7 +2,7 @@
 # your system. Help is available in the configuration.nix(5) man page, on
 # https://search.nixos.org/options and in the NixOS manual (`nixos-help`).
 
-{ config, lib, pkgs, inputs, ... }:
+{ config, lib, pkgs, inputs, outputs, ... }:
 
 {
   imports =
@@ -43,6 +43,7 @@
     config.allowUnfree = true;
     overlays = [
       inputs.nix-vscode-extensions.overlays.default
+      outputs.overlays.unstable-packages
     ];
   };