hydra: try to fix yggdrasil build

modules/nixos/services/hydra/default.nix

@@ -32,6 +32,9 @@ in
       port = cfg.httpPort;
       notificationSender = "hydra@localhost";
       useSubstitutes = true;
+      extraConfig = ''
+        allow-import-from-derivation = 1
+      '';
     };
   };
 }