tests/test-revert-flags.t

resourceutil: use `from importlib import resources`

Without this patch, we get the following error from when trying to run
hg with PyOxidizer:

  module 'importlib' has no attribute 'resources'

I don't know what why that happens, but `from importlib import
resources` is the form I would prefer anyway, so let's use that now
that the impoort-checker has been fixed.

Differential Revision: https://phab.mercurial-scm.org/D7701

#require execbit

  $ hg init repo
  $ cd repo
  $ echo foo > foo
  $ chmod 644 foo
  $ hg ci -qAm '644'

  $ chmod 755 foo
  $ hg ci -qAm '755'

reverting to rev 0

  $ hg revert -a -r 0
  reverting foo
  $ hg st
  M foo
  $ hg diff --git
  diff --git a/foo b/foo
  old mode 100755
  new mode 100644

  $ cd ..