Update Redis and related #2430

The call to `Redis.current` is deprecated and so we replace it with the default connection to Redis.

Now that we've cleared the deprecated method call, these two gems can be updated. They have to go together because Sidekiq locks to Redis.

We want to run Redis in CI rather than rely on the fake redis gem. We also want the major version of Redis to match that in production (7) locally and in CI.