[rubygems/rubygems] Bring TODO message up to date

https://github.com/rubygems/rubygems/commit/e07dba0923

lib/rubygems/ext/cargo_builder.rb

@@ -260,7 +260,7 @@ class Gem::Ext::CargoBuilder < Gem::Ext::Builder
 
       full_tmp_dest = File.join(extension_dir, tmp_dest_relative)
 
-      # TODO: remove in RubyGems 3
+      # TODO: remove in RubyGems 4
       if Gem.install_extension_in_lib && lib_dir
         FileUtils.mkdir_p lib_dir
         FileUtils.cp_r ext_path, lib_dir, remove_destination: true

lib/rubygems/ext/ext_conf_builder.rb

@@ -43,7 +43,7 @@ class Gem::Ext::ExtConfBuilder < Gem::Ext::Builder
 
       full_tmp_dest = File.join(extension_dir, tmp_dest_relative)
 
-      # TODO remove in RubyGems 3
+      # TODO remove in RubyGems 4
       if Gem.install_extension_in_lib and lib_dir
         FileUtils.mkdir_p lib_dir
         entries = Dir.entries(full_tmp_dest) - %w[. ..]