test_try_finally_raise fails on ubuntu-trusty with sage installed python 3.9

[kliem]

On older systems the test test_try_finally_signal fails:

https://github.com/kliem/cysignals/actions/runs/1498523090

[kliem]

The failing systems are those that have Sage install its own python. This might be the cause for the problem, I will see if I can figure it out.

For some reason the exception is not registered properly. The execution of the doctester is interrupted, but there is no exception set (and there #156 also doesn't reveal anything new).

I will see if the shebang line has anything to do with it (in src/scripts/cysignals-CSI):

#!/usr/bin/env python3

[kliem]

Perhaps the most revealing error message is

[cysignals-git]   Expecting:
[cysignals-git]       Traceback (most recent call last):
[cysignals-git]       ...
[cysignals-git]       RuntimeError: Aborted
[cysignals-git]   ok
[cysignals-git]   Trying:
[cysignals-git]       from cysignals.tests import *
[cysignals-git]   Expecting nothing
[cysignals-git]   ok
[cysignals-git]   sig_error() without sig_on()
[cysignals-git]   sig_error() without sig_on()
[cysignals-git]   sig_error() without sig_on()
[cysignals-git]   sig_error() without sig_on()
[cysignals-git]   killed by signal: 6

By https://github.com/kliem/cysignals/runs/4320680407?check_suite_focus=true