test(scaletest/workspacetraffic): fix test flake due to io.EOF on close#21231

mafredri merged 2 commits intomaincoder/coder:mainfrom

mafredri/test-fix-workspacetraffic-flakecoder/coder:mafredri/test-fix-workspacetraffic-flakeCopy head branch name to clipboard