…ls`` tries to execute a non-Python signal handler (pythonGH-24756)

We can receive signals (at the C level, in `trip_signal()` in signalmodule.c) while `signal.signal` is being called to modify the corresponding handler.  Later when `PyErr_CheckSignals()` is called to handle the given signal, the handler may be a non-callable object and would raise a cryptic asynchronous exception..
(cherry picked from commit 68245b7)

Co-authored-by: Antoine Pitrou <antoine@python.org>

pitrou deleted the backport-68245b7-3.8 branch

pitrou restored the backport-68245b7-3.8 branch

pitrou deleted the backport-68245b7-3.8 branch

pitrou restored the backport-68245b7-3.8 branch