[ruby/rubygems] Require stringio before use in default_system_gems helper

ruby/rubygems@c8f6a8ad8c

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hsbt

spec/bundler/support/helpers.rb

@@ -374,6 +374,7 @@ def installed_gems_list(options = {})
         require "rubygems/commands/list_command"
 
         # Capture output from the list command
+        require "stringio"
         output_io = StringIO.new
         cmd = Gem::Commands::ListCommand.new
         cmd.ui = Gem::StreamUI.new(StringIO.new, output_io, StringIO.new, false)