fix: don't add local cache to builder

common/modules/cachix.nix

@@ -1,8 +1,11 @@
 {
   config,
+  lib,
   pkgs,
   ...
-}: {
+}: let
+  inherit (lib) optionals;
+in {
   environment.systemPackages = [
     (pkgs.writeShellApplication {
       name = "rebuild-no-cache";
@@ -15,7 +18,8 @@
 
   nix = {
     settings = {
-      substituters = [
+      substituters =
+        [
           "https://hyprland.cachix.org"
           "https://nix-gaming.cachix.org"
           # Nixpkgs-Wayland
@@ -28,6 +32,8 @@
           "https://viperml.cachix.org"
           # Caddy
           "https://caddycf.cachix.org"
+        ]
+        ++ optionals (!config.services.nix-serve.enable) [
           # Personal config cache
           "https://cache.nelim.org"
         ];