FIX: better error message when forum is in read-only mode

app/controllers/export_csv_controller.rb

@@ -9,6 +9,8 @@ class ExportCsvController < ApplicationController
     Jobs.enqueue(:export_csv_file, entity: export_params[:entity], user_id: current_user.id, args: export_params[:args])
     StaffActionLogger.new(current_user).log_entity_export(export_params[:entity])
     render json: success_json
+  rescue Discourse::InvalidAccess
+    return render_json_error I18n.t("csv_export.rate_limit_error")
   end
 
   private