feat(server): enable ssh signature for forgejo repositories

modules/nixos/server/web-apps/forgejo/default.nix

@@ -24,11 +24,14 @@ in
     });
     services.forgejo = {
       enable = true;
-      settings.server = {
+      settings = {
+        server = {
           DOMAIN = cfg.url;
           ROOT_URL = "https://${cfg.url}/";
           HTTP_PORT = cfg.port;
         };
+        "repository.signing".FORMAT = "ssh";
+      };
     };
   };
 }