Disable the use of `gem update --system`, which is not supported when using
OpenBSD packages.  Also avoids printing the nagging update message:

  A new release of RubyGems is available: 3.4.1 - 3.4.2!
  Run `gem update --system 3.4.2` to update your installation.

The ENV usage is to skip this logic during tests, to avoid test failures.

Index: lib/rubygems.rb
--- lib/rubygems.rb.orig
+++ lib/rubygems.rb
@@ -1168,6 +1168,13 @@ An Array (#{env.inspect}) was passed in from #{caller[
 
     attr_accessor :disable_system_update_message
 
+    unless ENV['RUBYGEMS_SYSTEM_UPDATE_MESSAGE'] == 'enable'
+      Gem.disable_system_update_message = <<EOF
+Ruby was installed using an OpenBSD package, and using `gem update --system`
+is not supported.
+EOF
+    end
+
     ##
     # Whether RubyGems should enhance builtin `require` to automatically
     # check whether the path required is present in installed gems, and