[3.14] gh-156707: Do not follow junctions in os_helper.rmtree() on Windows (GH-156710) (GH-156715)

os.lstat() reports a junction as a directory, so the junction was followed
and files in the directory it points to could be removed.  Now the junction
itself is removed, as in os.walk() and shutil.rmtree().
(cherry picked from commit d87ee27)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Author: miss-islington

Lib/test/support/os_helper.py

@@ -433,7 +433,10 @@ def _rmtree_inner(path):
                           file=sys.__stderr__)
                     mode = 0
                 if stat.S_ISDIR(mode):
-                    _waitfor(_rmtree_inner, fullname, waitall=True)
+                    # Do not follow junctions, which os.lstat() reports
+                    # as directories.
+                    if not os.path.isjunction(fullname):
+                        _waitfor(_rmtree_inner, fullname, waitall=True)
                     _force_run(fullname, os.rmdir, fullname)
                 else:
                     _force_run(fullname, os.unlink, fullname)