Python's internal stderr may differ from sys.stderr.
When Python writes errors, it uses its internal stderr rather than the
overwritten sys.stderr.
This may not be the same file/handle
Fix the test to explicitly write to the specified stderr.
There is no indication this ever worked on windows as this is the first
test that checks python interactive console from a file.
Looking at the error from the CI, It closed the interpreter before
running any python commands.
Will reconfirm this when I have access to a windows machine.
From https://github.com/llvm/llvm-project/pull/174216
The cause is that in `python3.14`, `fcntl.ioctl` now throws a buffer
overflow error
when the buffer is too small or too large (see
https://github.com/python/cpython/pull/132919). This caused the Python
interpreter to fail terminal detection and not properly echo user
commands back to the screen.
Fix by dropping the custom terminal size check entirely and using the
built-in `sys.stdin.isatty()` instead.
Fixes#173302
