mistralclient set the endpoint_type invaild

Description
===========
when we set the endpoint_type in openrc. We set the "OS_MISTRAL_ENDPOINT_TYPE=internalURL" in the openrc file. Meanwhile，we don't set the "OS_MISTRAL_URL" in the openrc file. So we expected to visit the mistral by interURL.But we found it is invaild.

See the codes below(in mistralclient/auth/keystone.py):
            if not mistral_url:
                try:
                    mistral_url = session.get_endpoint(
                        service_type=service_type,
                        endpoint_type=endpoint_type,
                        region_name=region_name
                    )
                except Exception:
                    mistral_url = None

Environment
===========
Rocky version