nixos: add preferLocalBuild=true; on derivations for config files

nixos/modules/services/continuous-integration/buildkite-agent.nix

@@ -24,7 +24,7 @@ let
       EOF
       chmod 755 $out/${name}
     '';
-  in pkgs.runCommand "buildkite-agent-hooks" {} ''
+  in pkgs.runCommand "buildkite-agent-hooks" { preferLocalBuild = true; } ''
     mkdir $out
     ${concatStringsSep "\n" (mapAttrsToList mkHookEntry (filterAttrs (n: v: v != null) cfg.hooks))}
   '';

nixos/modules/services/continuous-integration/gitlab-runner.nix

@@ -8,6 +8,7 @@ let
     if (cfg.configFile == null) then
       (pkgs.runCommand "config.toml" {
         buildInputs = [ pkgs.remarshal ];
+        preferLocalBuild = true;
       } ''
         remarshal -if json -of toml \
           < ${pkgs.writeText "config.json" (builtins.toJSON cfg.configOptions)} \