Update docs and Rake task to require Redis 6

Since Redis 5 already reached EOL, let's drop support for it.

Changelog: changed

README.md

@@ -84,7 +84,7 @@ GitLab is a Ruby on Rails application that runs on the following software:
 - Ubuntu/Debian/CentOS/RHEL/OpenSUSE
 - Ruby (MRI) 3.0.5
 - Git 2.33+
-- Redis 5.0+
+- Redis 6.0+
 - PostgreSQL 12+
 For more information please see the [architecture](https://docs.gitlab.com/ee/development/architecture.html) and [requirements](https://docs.gitlab.com/ee/install/requirements.html) documentation.

lib/system_check/app/redis_version_check.rb

@@ -5,9 +5,7 @@
 module SystemCheck
   module App
     class RedisVersionCheck < SystemCheck::BaseCheck
-      # Redis 5.x will be deprecated
-      # https://gitlab.com/gitlab-org/gitlab/-/issues/331468
-      MIN_REDIS_VERSION = '5.0.0'
+      MIN_REDIS_VERSION = '6.0.0'
       RECOMMENDED_REDIS_VERSION = "6.0.0"
       set_name "Redis version >= #{RECOMMENDED_REDIS_VERSION}?"