Make Rake task check for Ruby 2.7.2

changelogs/unreleased/sh-require-ruby-2-7.yml

+---
+title: Update Rake check and docs to require Ruby 2.7
+merge_request: 48552
+author:
+type: changed

lib/system_check/app/ruby_version_check.rb

@@ -7,7 +7,7 @@ module SystemCheck
       set_check_pass -> { "yes (#{self.current_version})" }
 
       def self.required_version
-        @required_version ||= Gitlab::VersionInfo.new(2, 5, 3)
+        @required_version ||= Gitlab::VersionInfo.new(2, 7, 2)
       end
 
       def self.current_version