Bump redis from 4.1.4 to 4.2.1 (#14038)

Bump redis from 4.1.4 to 4.2.1 (#14038)

Bumps [redis](https://github.com/redis/redis-rb) from 4.1.4 to 4.2.1.
- [Release notes](https://github.com/redis/redis-rb/releases)
- [Changelog](https://github.com/redis/redis-rb/blob/master/CHANGELOG.md)
- [Commits](https://github.com/redis/redis-rb/compare/v4.1.4...v4.2.1)

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