Fix Pytest4.x warning about `message`
"message" parameter of pytest.raises is deprecated since Pytest4.1:
```
It is a common mistake to think this parameter will match the
exception message, while in fact it only serves to provide a custom
message in case the pytest.raises check fails.
```
That was the truth for test_unrecognised_attr_type_raises, which has
wrongly checked an exception message.
Fixes: https://pagure.io/freeipa/issue/7981
Signed-off-by: Stanislav Levin <slev@altlinux.org>
Reviewed-By: Christian Heimes <cheimes@redhat.com>