bpo-29798: Handle git worktree in make patchcheck (#629) (#633)

In git worktree directories, `.git` is a configuration file rather than a subdirectory (cherry picked from commit 6a6d090)

Author: ncoghlan

Tools/scripts/patchcheck.py

@@ -98,7 +98,10 @@ def changed_files(base_branch=None):
  cmd += ' --rev qparent'
  with subprocess.Popen(cmd.split(), stdout=subprocess.PIPE) as st:
  return [x.decode().rstrip() for x in st.stdout]
- elif os.path.isdir(os.path.join(SRCDIR, '.git')):
+ elif os.path.exists(os.path.join(SRCDIR, '.git')):
+ # We just use an existence check here as:
+ # directory = normal git checkout/clone
+ # file = git worktree directory
  if base_branch:
  cmd = 'git diff --name-status ' + base_branch
  else: