Forbid Sidekiq scheduling in transactions

Scheduling jobs in transactions can lead to race conditions where a job
runs before a transaction has been committed. The added initializer
ensures the various Sidekiq scheduling methods raise an error when
called inside a transaction.

Fixes #27233

config/initializers/forbid_sidekiq_in_transactions.rb

+module Sidekiq
+  module Worker
+    module ClassMethods
+      module NoSchedulingFromTransactions
+        NESTING = ::Rails.env.test? ? 1 : 0
+
+        %i(perform_async perform_at perform_in).each do |name|
+          define_method(name) do |*args|
+            if ActiveRecord::Base.connection.open_transactions > NESTING
+              raise <<-MSG.strip_heredoc
+                `#{self}.#{name}` cannot be called inside a transaction as this can lead to race
+                conditions when the worker runs before the transaction is committed and tries to
+                access a model that has not been saved yet.
+
+                Schedule the worker from inside a `run_after_commit` block instead.
+              MSG
+            end
+
+            super(*args)
+          end
+        end
+      end
+
+      prepend NoSchedulingFromTransactions
+    end
+  end
+end