full_text_mroonga_catalog: fix a PY3 regression

from 031408c6 (erp5_full_text_mroonga_catalog: defer fulltext index
and unindex using dedicated catalog keys., 2025-01-13)

bt5/erp5_full_text_mroonga_catalog/CatalogMethodTemplateItem/portal_catalog/erp5_mysql_innodb/SQLCatalog_deferUncatalogObjectActivity.py

 uid_list = []
 for grouped_message in grouped_message_list:
   assert not grouped_message.args
-  assert grouped_message.kw.keys() == ['uid']
+  assert len(grouped_message.kw) == 1
   uid_list.append(grouped_message.kw['uid'])
 for method_id in context.getSqlDeferredUncatalogObjectList():
   method = getattr(context, method_id)