Bump redis from 3.3.4 to 3.3.5 in /backend
Bump redis from 3.3.4 to 3.3.5 in /backend

Bumps [redis](https://github.com/andymccurdy/redis-py) from 3.3.4 to 3.3.5.
- [Release notes](https://github.com/andymccurdy/redis-py/releases)
- [Changelog](https://github.com/andymccurdy/redis-py/blob/master/CHANGES)
- [Commits](https://github.com/andymccurdy/redis-py/compare/3.3.4...3.3.5)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
patrick91/pycon,patrick91/pycon