Bug 40203: autoflush STDOUT in sign-nightly
We save logs of the sign-nightly script by redirecting STDOUT and STDERR to a file. However, when the output is not a terminal, STDOUT will have buffering by default, but STDERR will not, which results in some lines being written in the wrong order in our log file. To avoid that we enable autoflush on STDOUT.
Closes #40203 (closed).