(I'm still investigating at the moment whether something changed in my environment.)

Running the following right now hangs on test_input_tty for me:

./python.exe -m test test_builtin test_builtin -v


This fails on all branches up to and including 3.7, so I assume this is environment-specific unless it's a regression due to a change that was backported all the way back to 3.7, which is out of the question as the last functional commit on 3.7 was back in June.

Things I tried so far:
- rebooting;
- using another terminal app (I use iTerm2 by default, tried Terminal.app too);
- another shell (I use fish by default, tried bash 5.0 as well);
- a non-pydebug build (I use pydebug builds by default to run -R:)


The test in question is using deadline if available and `sysconfig.get_config_vars()['HAVE_LIBREADLINE']` returns 1. I'll be trying to check if that works for me next.