fix: try to fix export select

lib/tallty_import_export/export_form.rb

@@ -120,7 +120,7 @@ module TalltyImportExport
     end
 
     def export_headers_result **options
-      @headers = options.symbolize_keys[:headers]
+      @headers = options.deep_symbolize_keys[:headers]
       @headers = super(**options)
       @headers = TalltyImportExport::Attr::ExportHeader.new({ items: @headers })
     end