Bump redis-rb to version 5.0.8

Bump redis-rb to version 5.0.8

- Update redis/redis-rb from 5.0.7 to 5.0.8

The following dependencies have been updated by deps:

• redis/redis-rb from 5.0.7 to 5.0.8

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Changelog:

5.0.8
Fix Redis#without_reconnect for sentinel clients. Fix #1212.
Add sentinel_username, sentinel_password for sentinel clients. Bump redis-client to >=0.17.0. See #1213