Apply Rubocop Style/ExpandPathArguments (#23450)

config.ru

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 # This file is used by Rack-based servers to start the application.
 
-require ::File.expand_path('../config/environment', __FILE__)
+require ::File.expand_path('config/environment', __dir__)
 run Rails.application

spec/rails_helper.rb

@@ -1,5 +1,5 @@
 ENV['RAILS_ENV'] ||= 'test'
-require File.expand_path('../../config/environment', __FILE__)
+require File.expand_path('../config/environment', __dir__)
 
 abort("The Rails environment is running in production mode!") if Rails.env.production?