feat: use Array.wrap

lib/tallty_import_export/export.rb

@@ -70,9 +70,8 @@ module TalltyImportExport
           records.each do |record|
             context.record = record
             _export_association_headers = export_association_headers(**options)
-            _export_association_headers = _export_association_headers.is_a?(Array) ? _export_association_headers : [_export_association_headers]
-            _export_association_headers.each do |association_headers|
-              association_headers.with_indifferent_access!
+            Array.wrap(_export_association_headers).each do |association_headers|
+              association_headers = association_headers.with_indifferent_access
               association_records = record.send(association_headers[:association])
               sheet_name = if association_headers[:sheet_name].present?
                              association_headers[:sheet_name].respond_to?(:call) ?