Fix test by updating expected warning text

After
pypa/pip@1ee270a

Author: xavfernandez

Lib/test/test_venv.py

@@ -513,7 +513,7 @@ def do_test_with_pip(self, system_site_packages):
         #    executing pip with sudo, you may want sudo's -H flag."
         # where $HOME is replaced by the HOME environment variable.
         err = re.sub("^(WARNING: )?The directory .* or its parent directory "
-                     "is not owned by the current user .*$", "",
+                     "is not owned or is not writable by the current user.*$", "",
                      err, flags=re.MULTILINE)
         self.assertEqual(err.rstrip(), "")
         # Being fairly specific regarding the expected behaviour for the