Follow lean4-nix nixpkgs version

Author: samuelburnham

flake.lock

@@ -11,7 +11,10 @@
   };
 
   inputs = {
-    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    nixpkgs = {
+      url = "github:nixos/nixpkgs/nixos-unstable";
+      follows = "lean4-nix/nixpkgs";
+    };
     flake-parts.url = "github:hercules-ci/flake-parts";
     lean4-nix.url = "github:lenianiva/lean4-nix";
     blake3 = {