in_fluent_package_update_notifier: support multi worker

Author: Watson1978

lib/fluent/plugin/in_fluent_package_update_notifier.rb

@@ -40,6 +40,10 @@ class FluentPackageUpdateNotifierInput < Fluent::Plugin::Input
       desc "Package repository site"
       config_param :repository_sites, :array, default: ["https://packages.treasuredata.com"]
 
+      def multi_workers_ready?
+        true
+      end
+
       def configure(conf)
         super
       end

test/plugin/test_in_fluent_package_update_notifier.rb

@@ -30,6 +30,11 @@ def config
     ]
   end
 
+  test "multi worker" do
+    d = create_driver
+    assert_true d.instance.multi_workers_ready?
+  end
+
   sub_test_case "configuration test" do
     test "default configuration" do
       assert_nothing_raised do