`translate_error` doesn't handle errors that are strings not JSON

[apdavison]

This seems to be 500 errors, in particular.

e.g.

../../env/lib/python3.8/site-packages/kg_core/response.py:198: in translate_error
    return Error(**response.content["error"]) if response.content and "error" in response.content and response.content[
E   TypeError: ModelMetaclass object argument after ** must be a mapping, not str

(Pdb) response.content
{'timestamp': '2022-08-29T08:23:19.604+00:00', 'status': 500, 'error': 'Internal Server Error', 'message': '', 'path': '/v3-beta/instances'}

[olinux]

fixed in 0.9.9