Bump pin on redis to allow > 8.0.0

[redis](https://pypi.org/project/redis/) released 8.0.1, but google-cloud-ndb is limited to less than 7.0.0. https://github.com/googleapis/python-ndb/blob/a441cea83bd9b6f5c88e822746cb23ca192e010b/setup.py#L48