Since the upgrade to giac 1.5 (#26315) the test suite for sage.interfaces.giac will sometimes randomly hang.

I don't have a reliable way to reproduce the problem: I just run

./sage -t --long src/sage/interfaces/giac.py

in an infinitely loop, and once out of roughly every 5 runs the test process will just hang without any CPU usage, usually on completely arbitrary lines in the test. Though the test process will at least respond to being killed with a SIGTERM so the issue probably isn't a threading deadlock in openblas, at last (those tend to be unresponsive to signals in Cygwin since it's using Windows native threads directly).

CC: @frederichan-IMJPRG @sagetrac-parisse @slel

Component: interfaces

Keywords: giac

Author: Erik Bray

Branch: 8d0a9df

Reviewer: Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/27385