test_pyrepl.test_repl_eio is flaky on some machines

[cmaloney]

Bug report

Bug description:

Flakiness reports: #135329 (comment) (Github CI UBSan build)
Test added in gh-135329

From that flakiness report:

test test_pyrepl failed -- Traceback (most recent call last):
  File "/home/runner/work/cpython/cpython/Lib/test/test_pyrepl/test_unix_console.py", line 390, in test_repl_eio
    _, err = proc.communicate(timeout=support.LONG_TIMEOUT)
             ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/cpython/cpython/Lib/subprocess.py", line 1273, in communicate
    stdout, stderr = self._communicate(input, endtime, timeout)
                     ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/cpython/cpython/Lib/subprocess.py", line 2293, in _communicate
    self._check_timeout(endtime, orig_timeout, stdout, stderr)
    ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/cpython/cpython/Lib/subprocess.py", line 1320, in _check_timeout
    raise TimeoutExpired(
    ...<2 lines>...
            stderr=b''.join(stderr_seq) if stderr_seq else None)
subprocess.TimeoutExpired: Command '['/home/runner/work/cpython/cpython/python', '-E', '-S', '/home/runner/work/cpython/cpython/Lib/test/test_pyrepl/eio_test_script.py']' timed out after 300.0 seconds

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response