Fixed a test that could fail depending on PASSWORD_HASHERS.

    @override_settings(PASSWORD_HASHERS=('django.contrib.auth.tests.test_auth_backends.CountingMD5PasswordHasher',))

    def test_authentication_timing(self):

        """Hasher is run once regardless of whether the user exists. Refs #20760."""

        # Re-set the password, because this tests overrides PASSWORD_HASHERS

        self.user.set_password('test')

        self.user.save()

        CountingMD5PasswordHasher.calls = 0

        username = getattr(self.user, self.UserModel.USERNAME_FIELD)

        authenticate(username=username, password='test')