Revert "Temporarily allow sidekiq warning"

This reverts commit e2c5814.

Sidekiq has since released a version with the fix

Author: Earlopain

activesupport/lib/active_support/testing/strict_warnings.rb

@@ -10,8 +10,6 @@ class WarningError < StandardError; end
     PROJECT_ROOT = File.expand_path("../../../../", __dir__)
     ALLOWED_WARNINGS = Regexp.union(
       /circular require considered harmful.*delayed_job/, # Bug in delayed job.
-      # TODO: Remove with the next sidekiq version bump
-      /circular require considered harmful.*sidekiq/,
 
       # Expected non-verbose warning emitted by Rails.
       /Ignoring .*\.yml because it has expired/,