Fix wrong use of identity operation

Strings should not be compared with the identity operation 'is' or
'is not'.

Fixes: https://pagure.io/freeipa/issue/8057
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>

ipatests/test_ipaserver/test_ldap.py

@@ -233,7 +233,7 @@ class test_LDAPEntry:
         e = self.entry
         assert e.pop('cn') == self.cn1
         assert 'cn' not in e
-        assert e.pop('cn', 'default') is 'default'
+        assert e.pop('cn', 'default') == 'default'
         with pytest.raises(KeyError):
             e.pop('cn')