Restore child interrupt mask reset

Assisted-By: devx/3236e566-7538-432e-a30a-2bdf37265ed4

Author: samuel-williams-shopify

lib/async/container/threaded.rb

@@ -114,7 +114,9 @@ def exec(*arguments, ready: true, **options)
 				def self.fork(**options)
 					self.new(**options) do |thread|
 						::Thread.new do
-							yield Instance.for(thread)
+							::Thread.handle_interrupt(SignalException => :immediate) do
+								yield Instance.for(thread)
+							end
 						end
 					end
 				end