Update /openapi-python-client to version 0.26 or higher

[ckunki]

Version 0.26 of openapi-python-client introduced default responses,

This unfortunately revealed a bug in the implementation of the Exasol SaaS REST API.

See IntRef and CI Build log:

with testee.database(database_name, ignore_delete_failure=True) as db:

/usr/lib/python3.12/contextlib.py:144: in __exit__
    next(self.gen)
exasol/saas/client/api_access.py:299: in database
    response = self.delete_database(db.id, ignore_delete_failure)
exasol/saas/client/api_access.py:271: in delete_database
    return delete_database.sync_detailed(
exasol/saas/client/openapi/api/databases/delete_database.py:87: in sync_detailed
    return _build_response(client=client, response=response)
exasol/saas/client/openapi/api/databases/delete_database.py:55: in _build_response
    parsed=_parse_response(client=client, response=response),
exasol/saas/client/openapi/api/databases/delete_database.py:43: in _parse_response
    response_default = ApiError.from_dict(response.json())

cls = <class 'exasol.saas.client.openapi.models.api_error.ApiError'>
src_dict = {'code': 404, 'handler': 'saas-api-service-databases-staging-deleteDatabase', 
'logId': '2025/10/27/[$LATEST]e2439ded012e467cabfbd39d3fe7254f',
 'message': 'Could not find database with id: 4oJGtNv_SPq-DckM4FgHgg', ...}

    @classmethod
    def from_dict(cls: type[T], src_dict: Mapping[str, Any]) -> T:
        d = dict(src_dict)
>       status = d.pop("status")
E       KeyError: 'status'

exasol/saas/client/openapi/models/api_error.py:92: KeyError