py3: fix doctests in doctest/test

[mwageringel]

This ticket fixes the last Python 3 doctest failure in doctest/test.py.

The problem is that the doctest dispatcher relies on internals of the multiprocessing library, which slightly changed in Python 3; see the relevant file. Because of that, until now with Python 3, the master doctest process waits for its children to exit before exiting itself, even though it is not supposed to.

I also adjusted the affected doctest so that it checks for what was initially intended. This got lost when the minimum die_timeout of subprocesses got increased from 20 to 60 seconds, but this also means the doctest now lasts 40 seconds longer than before.

Component: python3

Author: Markus Wageringel

Branch/Commit: 4be8c5d

Reviewer: John Palmieri

Issue created by migration from https://trac.sagemath.org/ticket/28232

[mwageringel]

New commits:

4be8c5d

28232: py3: do not wait for subprocesses on exit

[mwageringel]

Commit: 4be8c5d

[mwageringel]

Author: Markus Wageringel

[mwageringel]

Branch: u/gh-mwageringel/28232

[jhpalmieri]

comment:2

Nice work. Looks good to me.

[jhpalmieri]

Reviewer: John Palmieri

[vbraun]

Changed branch from u/gh-mwageringel/28232 to 4be8c5d