DEV: Ensure Sidekiq warnings are logged to STDERR (#15800)

The default configuration will log to STOUT, which pollutes the output of scripts/rake-tasks

config/initializers/100-sidekiq.rb

@@ -81,7 +81,7 @@ if Sidekiq.server?
   end
 end
 
-Sidekiq.logger.level = Logger::WARN
+Sidekiq.logger = Sidekiq::Logger.new(STDERR, level: Logger::WARN)
 
 class SidekiqLogsterReporter < Sidekiq::ExceptionHandler::Logger
   def call(ex, context = {})

lib/demon/sidekiq.rb

@@ -31,7 +31,7 @@ class Demon::Sidekiq < ::Demon::Base
     # trouble, if STDOUT is closed in our process all sort of weird
     # will ensue, resetting the logger ensures it will reinit correctly
     # parent process is in charge of the file anyway.
-    Sidekiq.logger = nil
+    Sidekiq.logger = Sidekiq::Logger.new(STDERR, level: Logger::WARN)
     cli = Sidekiq::CLI.instance
 
     # Unicorn uses USR1 to indicate that log files have been rotated