Require irb gem for an initializer

Rails 7.1 start explicitly adding this gem as a dependency.
We don't have it in Gemfile, so let's explicityl require it.

config/initializers/irb.rb

 # frozen_string_literal: true
 
+require 'irb'
+
 if Gitlab::Runtime.console?
   # Stop irb from writing a history file by default.
   module IrbNoHistory