Don't memoize interruption adapter

Some tests rely on changing the interruption adapter mid-execution to test specific behaviour. We shouldn't break that with this feature.

lib/job-iteration/iteration.rb

@@ -75,10 +75,6 @@ def around_iterate(&blk)
         set_callback(:iterate, :around, &blk)
       end
 
-      def interruption_adapter
-        JobIteration.interruption_adapter || JobIteration::InterruptionAdapters.lookup(queue_adapter_name)
-      end
-
       private
 
       def ban_perform_definition
@@ -93,7 +89,6 @@ def initialize(*arguments)
       self.times_interrupted = 0
       self.total_time = 0.0
       assert_implements_methods!
-      @interruption_adapter = self.class.interruption_adapter
     end
     ruby2_keywords(:initialize) if respond_to?(:ruby2_keywords, true)
 
@@ -125,8 +120,9 @@ def retry_job(*, **)
 
     private
 
-    # @api private
-    attr_reader :interruption_adapter
+    def interruption_adapter # @private
+      JobIteration.interruption_adapter || JobIteration::InterruptionAdapters.lookup(self.class.queue_adapter_name)
+    end
 
     def enumerator_builder
       JobIteration.enumerator_builder.new(self)