Python raises a `TypeError` if you try to (re-)install a C signal handler

[smurfix]

Closes #2333.

[codecov[bot]]

Codecov Report

Merging #2334 (55af19e) into master (9d2bad1) will increase coverage by 1.08%. The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2334      +/-   ##
==========================================
+ Coverage   97.89%   98.97%   +1.08%     
==========================================
  Files         117      117              
  Lines       16119    16119              
  Branches     3122     3122              
==========================================
+ Hits        15779    15954     +175     
+ Misses        281      116     -165     
+ Partials       59       49      -10     

Impacted Files	Coverage Δ
trio/_util.py	100.00% <100.00%> (ø)
trio/tests/test_ssl.py	99.86% <0.00%> (+0.55%)	:arrow_up:
trio/tests/test_socket.py	100.00% <0.00%> (+0.65%)	:arrow_up:
trio/_core/_io_windows.py	98.76% <0.00%> (+0.92%)	:arrow_up:
trio/_core/_run.py	100.00% <0.00%> (+0.99%)	:arrow_up:
trio/_core/tests/test_io.py	100.00% <0.00%> (+1.05%)	:arrow_up:
trio/tests/test_highlevel_open_tcp_stream.py	100.00% <0.00%> (+1.47%)	:arrow_up:
trio/_core/_multierror.py	100.00% <0.00%> (+3.70%)	:arrow_up:
trio/_subprocess_platform/__init__.py	100.00% <0.00%> (+5.71%)	:arrow_up:
trio/_highlevel_ssl_helpers.py	100.00% <0.00%> (+11.76%)	:arrow_up:
... and 5 more

[smurfix]

I have no idea why these test failures happen, but they're very unlikely to be from my change.

[pquentin]

They're not, I'm looking into them in https://github.com/python-trio/trio/pull/2332