SYDNEY, Aug 28 (Reuters) - Friends of detained Australian writer Yang Hengjun, put on trial in Beijing two years ago on undisclosed national security charges, say they fear for his health amid delays in a verdict in his case. Pro-democracy blogger Yang is an Australian citizen born in China who was working in New York before his arrest at Guangzhou airport in 2019. His arrest coincided with a deterioration in relations between Australia and China and a verdict in his case has been repeatedly delayed. A Beijing court heard Yang's trial in secret in May 2021 and the case against...