Fix eval warning: stdenv.hostPlatform.system

flake.nix

@@ -26,7 +26,7 @@
 
     nixosModules = {
       default = { lib, pkgs, config, ... }: let
-        sso-bsn = self.packages.${pkgs.system}.default;
+        sso-bsn = self.packages.${pkgs.stdenv.hostPlatform.system}.default;
         gen-secret = pkgs.writeShellScript "gen-secret" ''
           (umask 077; [ -f $1/$2 ] || ${pkgs.coreutils}/bin/head -c 128 /dev/urandom | ${pkgs.coreutils}/bin/base64 -w0 > $1/$2)
         '';