Upgrade redis-store and redis-activesupport

What does this MR do?

These upgrades are needed so that these gems support Rails 6.

We held off on these upgrades because of: !18969 (comment 236215696)

Now that the bug is fixed upstream this should be safe to upgrad.

Also, since !19202 (merged) was merged we don't use redis-activesupport anymore. We still need to keep this though since this is part of redis-rails and we use the session store in redis-actionpack.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

#33408 (closed)