This would be in addition to the existing test environments that use Docker.

https://us.images.linuxcontainers.org/

Depends on #31831

CC: @dimpase @novoselt @sagetrac-tmonteil

Component: porting

Branch/Commit: u/mkoeppe/tox_ini__add_test_environments_using_lxc @ 7e1cb19

Issue created by migration from https://trac.sagemath.org/ticket/29283