tests/test-dirstate-backup.t

pytype: stop excluding upgrade.py

The sole failure here was this, which is fixed by simply creating a set like the
caller, instead of a dict:

  File "/mnt/c/Users/Matt/hg/mercurial/upgrade.py", line 73, in upgraderepo:
      No attribute 'discard' on Dict[nothing, nothing] [attribute-error]
    In Union[Any, Dict[nothing, nothing]]

Differential Revision: https://phab.mercurial-scm.org/D11911

Set up

  $ hg init repo
  $ cd repo

Try to import an empty patch

  $ hg import --no-commit - <<EOF
  > EOF
  applying patch from stdin
  abort: stdin: no diffs found
  [10]

No dirstate backups are left behind

  $ ls .hg/dirstate* | sort
  .hg/dirstate