test: fix warning In function ‘send_a_byte_cb’: test/regress.c:1853:2: warning: ignoring return value of ‘write’, declared with attribute warn_unused_result [-Wunused-result] (void) write(*sockp, "A", 1); (cherry picked from commit 56010f37ae5b49881f7fd255d5c8a936e1c36909)