Bump recommended Redis version from 4.0 to 5.0

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

changelogs/unreleased/327197-deprecate-redis-4-on-rake-gitlab-check.yml

+---
+title: Bump recommended Redis version from 4.0 to 5.0
+merge_request: 59072
+author: Takuya Noguchi
+type: deprecated

lib/system_check/app/redis_version_check.rb

@@ -5,8 +5,10 @@ require 'redis'
 module SystemCheck
   module App
     class RedisVersionCheck < SystemCheck::BaseCheck
+      # Redis 4.x will be deprecated
+      # https://gitlab.com/gitlab-org/gitlab/-/issues/327197
       MIN_REDIS_VERSION = '4.0.0'
-      RECOMMENDED_REDIS_VERSION = '4.0.0' # In future we may deprecate but still support Redis 4
+      RECOMMENDED_REDIS_VERSION = '5.0.0'
       set_name "Redis version >= #{RECOMMENDED_REDIS_VERSION}?"
 
       @custom_error_message = ''