switch main branch to unstable, add a check to ensure nixpkgs input has consistent format

Author: nzbr

checks/nixpkgs-input.nix

@@ -0,0 +1,8 @@
+{ runCommand
+, gnugrep
+, ...
+}:
+runCommand "check-nixpkgs-input" { } ''
+  ${gnugrep}/bin/grep -E 'nixpkgs.url *= *"github:NixOS/nixpkgs/nixos-(unstable|[0-9]+.[0-9]+)";' ${./../flake.nix}
+  touch $out
+''

flake.lock

@@ -2,7 +2,7 @@
   description = "NixOS WSL";
 
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.11";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
 
     flake-compat = {
       url = "github:edolstra/flake-compat";
@@ -78,6 +78,7 @@
         {
           dotnet-format = pkgs.callPackage ./checks/dotnet-format.nix args;
           nixpkgs-fmt = pkgs.callPackage ./checks/nixpkgs-fmt.nix args;
+          nixpkgs-input = pkgs.callPackage ./checks/nixpkgs-input.nix args;
           rustfmt = pkgs.callPackage ./checks/rustfmt.nix args;
           side-effects = pkgs.callPackage ./checks/side-effects.nix args;
           username = pkgs.callPackage ./checks/username.nix args;