Fix Ruby 3.0+ compatibility in test suite

Ruby 3.0 no longer auto-loads Logger from the standard library.
ActiveSupport 6.1 expects it to be available, causing tests to fail
with "uninitialized constant ActiveSupport::LoggerThreadSafeLevel::Logger".

Author: tf

spec/rails_helper.rb

@@ -1,5 +1,6 @@
 ENV['RAILS_ENV'] ||= 'test'
 
+require 'logger'
 require 'combustion'
 Combustion.initialize!(:active_record, :action_controller, :action_view, :sprockets)