The testreport log files, such as https://autobuilder.yocto.io/pub/non-release/20211002-17/testresults/qemuarm64-ptest/valgrind.log, are served as Content-Type: application/octet-stream. This is a pain when reading the logs as you need to download them and open in a text editor. If they were sent as text/plain then they could be read in the browser.
I've set ".log" files to the text/plain mime-type. Please reopen the bug if it doesn't work as desired.