test(active_job): use def instead of define_method to avoid JRuby DynamicScope NPE

Author: solnic

sentry-rails/spec/active_job/shared_examples/argument_serialization.rb

@@ -61,7 +61,7 @@ def event_arguments
     post = Post.create!
 
     problematic_job = job_fixture do
-      define_method(:perform) do |passed_post|
+      def perform(passed_post)
         def passed_post.to_global_id
           raise "intentional"
         end
@@ -82,7 +82,7 @@ def passed_post.to_global_id
     mod = Module.new
 
     module_job = job_fixture do
-      define_method(:perform) do |_mod|
+      def perform(_mod)
         raise "boom from argument_serialization spec"
       end
     end