[3.12] gh-117503: Fix test for posixpath.expanduser() when pw_dir ends with / (GH-118056) (GH-118058)

(cherry picked from commit ccdcd1d)

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

Author: miss-islington

Lib/test/test_posixpath.py

@@ -341,6 +341,7 @@ def test_expanduser_pwd2(self):
         for e in pwd.getpwall():
             name = e.pw_name
             home = e.pw_dir
+            home = home.rstrip('/') or '/'
             self.assertEqual(posixpath.expanduser('~' + name), home)
             self.assertEqual(posixpath.expanduser(os.fsencode('~' + name)),
                              os.fsencode(home))