ci: remove reference to mock object after test

This patch should fix #5054

Signed-off-by: Shizuo Fujita <[email protected]>

Author: Watson1978

test/plugin/test_input.rb

@@ -133,5 +133,7 @@ def emit(tag, es)
     assert{ @p.router.object_id != original_router.object_id }
 
     @p.router.emit('mytag.testing', ['for mock'])
+  ensure
+    Fluent::Engine.root_agent.labels['@mytest'] = nil
   end
 end

test/plugin_helper/test_event_emitter.rb

@@ -70,6 +70,8 @@ class Dummy < Fluent::Plugin::TestBase
     d.configure(config_element('ROOT', '', {'@label' => '@mytest'}))
     router = d.event_emitter_router("@mytest")
     assert_equal router_mock, router
+  ensure
+    Fluent::Engine.root_agent.labels['@mytest'] = nil
   end
 
   test 'get root router' do