tests/test-revert-unknown.t

contrib: install latest versions of Python

Let's keep our build environment modern.

We upgrade 3.5-3.8 on Linux. Just 3.7 and 3.8 on Windows because we
don't use <3.7 on Windows.

Differential Revision: https://phab.mercurial-scm.org/D9145

  $ hg init
  $ touch unknown

  $ touch a
  $ hg add a
  $ hg ci -m "1"

  $ touch b
  $ hg add b
  $ hg ci -m "2"

Should show unknown

  $ hg status
  ? unknown
  $ hg revert -r 0 --all
  removing b

Should show unknown and b removed

  $ hg status
  R b
  ? unknown

Should show a and unknown

  $ ls -A
  .hg
  a
  unknown