tadpole: Assert that nginx is running when using gitea

hosts/tadpole/modules/gitea/default.nix

@@ -7,8 +7,6 @@
 let
   conf = config.mod.gitea;
   gitDomain = "git.${conf.baseDomain}";
-
-  nginxEnable = config.mod.nginx.enable;
 in
 {
   options = {
@@ -37,8 +35,12 @@ in
     };
   };
 
-  config = lib.mkIf (conf.enable && nginxEnable) {
+  config = lib.mkIf conf.enable {
     assertions = [
+      {
+        assertion = config.services.nginx.enable;
+        message = "Option 'config.services.nginx' must be enabled";
+      }
       {
         assertion = conf.baseDomain != "";
         message = "Option 'mod.gitea.baseDomain' cannot be empty";