Use a more reliable way to detect current Ruby version

changelogs/unreleased/46950-systemcheck-ruby-version.yml

+---
+title: 'SystemCheck: Use a more reliable way to detect current Ruby version'
+merge_request: 23291
+author:
+type: changed

lib/system_check/app/ruby_version_check.rb

@@ -11,7 +11,7 @@ module SystemCheck
       end
 
       def self.current_version
-        @current_version ||= Gitlab::VersionInfo.parse(Gitlab::TaskHelpers.run_command(%w(ruby --version)))
+        @current_version ||= Gitlab::VersionInfo.parse(RUBY_VERSION)
       end
 
       def check?