fix: add require 'set' for Ruby < 3.2 compatibility

Author: ahogappa

lib/irb/init.rb

@@ -4,6 +4,8 @@
 #   	by Keiju ISHITSUKA(keiju@ruby-lang.org)
 #
 
+require 'set'
+
 module IRB # :nodoc:
   @CONF = {}
   @INITIALIZED = false
@@ -197,6 +199,10 @@ def IRB.init_config(ap_path)
     }
 
     @CONF[:COPY_COMMAND] = ENV.fetch("IRB_COPY_COMMAND", nil)
+
+    @CONF[:RELOADABLE_REQUIRE] = false
+    @CONF[:__RELOADABLE_FILES__] = Set.new
+    @CONF[:__AUTOLOAD_FILES__] = Set.new
   end
 
   def IRB.set_measure_callback(type = nil, arg = nil, &block)