nixos/roundcube: nginx config for max attachment size

Fixes #506235

Not sure if I mistested this in #51304 or something changed
in the mean time. Moving it to `location./` is not sufficient.

nixos/modules/services/mail/roundcube.nix

@@ -199,10 +199,11 @@ in
               fastcgi_param PATH_INFO $fastcgi_path_info;
               fastcgi_split_path_info ^(.+\.php)(/.+)$;
               include ${config.services.nginx.package}/conf/fastcgi.conf;
-
-              client_max_body_size ${toString cfg.maxAttachmentSize};
             '';
           };
+          extraConfig = ''
+            client_max_body_size ${toString cfg.maxAttachmentSize};
+          '';
         };
       };
     };