fixes #1594

[KeremTurgutlu]

nbdev-test fails with the following error, because faulthandler.register by default uses sys.stderr and it gets changed in execnb ipykernel environment. This PR sets file=sys.__stderr__ which is the source terminal.

(uvws) ~/aai-ws/nbdev (main ✔) nbdev-test
UnsupportedOperation in /Users/keremturgutlu/aai-ws/nbdev/nbs/api/12_test.ipynb:
===========================================================================

While Executing Cell #6:
Traceback (most recent call last):
  File "/Users/keremturgutlu/aai-ws/nbdev/nbdev/test.py", line 55, in test_nb
    k.run_all(nb, exc_stop=True, preproc=_no_eval, verbose=verbose)
  File "/Users/keremturgutlu/aai-ws/execnb/execnb/shell.py", line 252, in run_all
    if self.exc and exc_stop: raise self.exc from None
                              ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/keremturgutlu/aai-ws/.venv/lib/python3.12/site-packages/IPython/core/interactiveshell.py", line 3748, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-1-a46277746112>", line 2, in <module>
    success,duration = test_nb(_nb, skip_flags=['notest'])
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<ipython-input-1-058ebeb728be>", line 11, in test_nb
    faulthandler.register(signal.SIGINT, all_threads=True, chain=True)
io.UnsupportedOperation: fileno