tests hanging on MacOS

[bretello]

Tests are currently hanging on MacOS possibly due to termios. Here's a minimal example to reproduce the issue:

import os
import termios
import time
from threading import Thread

device_fd, tty_fd = os.openpty()


def loop():
    print("starting read loop")
    while True:
        print(".", end="")
        data = os.read(device_fd, 1)
        print(f"got {data=}")  # <--- never gets here
        time.sleep(0.1)


thread = Thread(target=loop, daemon=True)
thread.start()

os.write(tty_fd, b"123")
termios.tcdrain(tty_fd)  # <--- gets stuck here
time.sleep(3)  # allow thread to read all data

For some more context see 9330c33 and python/cpython#97001