By Matt Hardy The country’s governing swimming body Aquatics GB has said it is “extremely concerned” by 23 Chinese athletes being cleared to compete at Tokyo 2020 despite testing positive for a banned substance before the Olympics. The swimmers tested positive for trimetazidine (TMZ), which is a heart medication used to prevent angina attacks, at a training camp before the last Olympics, which were delayed until 2021 due to the Covid-19 pandemic. “We are extremely concerned by allegations concerning positive tests in the build-up to the Tokyo Olympics Games which were reported over the weekend…