.gitlab-ci.yml: make test command consistent across distros

This switches to use "python3 -m unittest discover -v" onevery distro.
11 jobs for patch-1 in 5 minutes and 26 seconds (queued for 4 seconds)
Status Name Job ID Coverage
  Linting
passed linting:bandit #117556

00:00:38

passed linting:codespell #117557

00:00:52

passed linting:mypy #117560

00:00:55

passed linting:pyflakes #117559

00:00:37

passed linting:pylint #117558

00:00:52

 
  Test
passed tests:archlinux #117561

00:02:33

passed tests:debian #117562

00:02:17

failed tests:debian_with_bubblewrap #117563

00:00:52

passed tests:fedora #117564

00:02:34

failed tests:gentoo #117566

00:01:55

failed tests:gentoo #117565

00:00:54

 
Name Stage Failure
failed
tests:gentoo Test
No job log
failed
tests:debian_with_bubblewrap Test
No job log