Update rubocop to version 1.69.1 (#32967)

lib/mastodon/cli/progress_helper.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-dev_null = Logger.new('/dev/null')
+dev_null = Logger.new(File::NULL)
 
 Rails.logger                 = dev_null
 ActiveRecord::Base.logger    = dev_null

lib/tasks/mastodon.rake

@@ -592,7 +592,7 @@ namespace :mastodon do
 end
 
 def disable_log_stdout!
-  dev_null = Logger.new('/dev/null')
+  dev_null = Logger.new(File::NULL)
 
   Rails.logger                 = dev_null
   ActiveRecord::Base.logger    = dev_null