ci: jobs now hang somewhat regularly after enabling python 3.13 tests

[cpcloud]

https://github.com/ibis-project/ibis/actions/runs/12990636602/job/36226330020?pr=10729

AFAICT it's limited to python 3.13 as well.

[cpcloud]

Seems like it might not be specific to postgres/psycopg and more related to Python 3.13. Here's an MS SQL test run hanging indefinitely: https://github.com/ibis-project/ibis/actions/runs/13001091981/job/36259761771?pr=10735

[cpcloud]

Ok, it's not specific to python 3.13, here's a postgres run with python 3.10.

I'm going to disable running tests in parallel and see if that helps.

[cpcloud]

This seems to have been mitigated by more aggressive connection clean up in tests.