(Refiles to fix garble in headline) SHANGHAI (Reuters) – Shanghai carried out another round of mass COVID-19 testing on Saturday, this time testing residents at least twice in a single day, as a city official in China’s financial hub acknowledged shortcomings in the handling of the outbreak. It was the fourth consecutive day of city-wide testing in Shanghai, which reported a record 23,600 new locally transmitted cases. While those case numbers are small by global standards, the city has become a test bed for the country’s elimination strategy, which seeks to test, trace and centrally quarantin…