nixpkgs-update: Disable post build hook with a patch

We want to avoid pushing to multiple cachix caches and r-ryantm has
it's own already.

build01/nixpkgs-update-disable-post-build-hook.patch

@@ -0,0 +1,16 @@
+diff --git a/src/Utils.hs b/src/Utils.hs
+index 00e539e..461b234 100644
+--- a/src/Utils.hs
++++ b/src/Utils.hs
+@@ -252,7 +252,10 @@ nixBuildOptions =
+     "true",
+     "--option",
+     "restrict-eval",
+-    "true"
++    "true",
++    "--option",
++    "post-build-hook",
++    "/run/current-system/sw/bin/true"
+   ]
+     <> nixCommonOptions
+ 

build01/nixpkgs-update.nix

@@ -4,7 +4,12 @@ let
   userLib = import ../users/lib.nix { inherit lib; };
 
   sources = import ../nix/sources.nix;
-  nixpkgs-update = import sources.nixpkgs-update {};
+  nixpkgs-update = (import sources.nixpkgs-update {}).overrideAttrs(old: {
+    patches = old.patches or [] ++ [
+      ./nixpkgs-update-disable-post-build-hook.patch
+    ];
+  });
+
   nixpkgsUpdateSystemDependencies = with pkgs; [
     nix
     git