nixos/workflows: reclassify as private modules

It doesn't fit with the public module requirement of no reliance of
third-party modules anymore as we'll be using Bahaghari at the near future.

modules/nixos/_private/default.nix

@@ -9,5 +9,6 @@
     ./suites/i18n.nix
     ./suites/server.nix
     ./suites/vpn.nix
+    ./workflows
   ];
 }

modules/nixos/default.nix

@@ -13,6 +13,5 @@
     ./services/vouch-proxy.nix
     ./services/yt-dlp.nix
     ./tinted-theming.nix
-    ./workflows
   ];
 }