Make test timeout more informatively on macos CI

[ogrisel]

test_parallel_with_interactively_defined_functions_default_backend happens to be killed from time to time on the slow macos CI host and the error message was not informative.

Using faulthandler in the subprocess script instead should help although I suspect that this wasn't really a deadlock but that the previous 5s timeout was too short for the slow CI host.

Let's see.

[codecov]

Codecov Report

Base: 94.00% // Head: 93.89% // Decreases project coverage by -0.10% ⚠️

Coverage data is based on head (85f61a1) compared to base (54f4d21).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1332      +/-   ##
==========================================
- Coverage   94.00%   93.89%   -0.11%     
==========================================
  Files          52       52              
  Lines        7301     7303       +2     
==========================================
- Hits         6863     6857       -6     
- Misses        438      446       +8     

Impacted Files	Coverage Δ
joblib/test/test_parallel.py	97.05% <100.00%> (ø)
joblib/testing.py	95.23% <100.00%> (+0.23%)	⬆️
joblib/test/testutils.py	50.00% <0.00%> (-50.00%)	⬇️
joblib/_parallel_backends.py	93.01% <0.00%> (-1.84%)	⬇️

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