Merge branch 'ps/ci-misc-updates'

Merge branch 'ps/ci-misc-updates'

CI updates (containerization, dropping stale ones, etc.).

* ps/ci-misc-updates:
  ci: remove stale code for Azure Pipelines
  ci: use latest Ubuntu release
  ci: stop special-casing for Ubuntu 16.04
  gitlab-ci: add linux32 job testing against i386
  gitlab-ci: remove the "linux-old" job
  github: simplify computation of the job's distro
  github: convert all Linux jobs to be containerized
  github: adapt containerized jobs to be rootless
  t7422: fix flaky test caused by buffered stdout
  t0060: fix EBUSY in MinGW when setting up runtime prefix