Add integration tests to gitlab CI

.gitlab-ci.yml:
Rename "lint" stage to "test" stage.
Change basic target to also update the pacman files databases, as they
are required for integration tests.
Add integration target to run `tox -e integration`.
3 jobs for issues/9 in 4 minutes and 7 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed #17670
coverage

00:00:45

passed #17671
integration

00:04:06

passed #17669
linter

00:00:48