Fix ActionPack tests after changes to missing template logger

After merging #19377 ActionPack tests were missing a require for
`ActiveSupport::LogSubscriber::TestHelper` and change didn't take
into account that logger could be nil. Added the require and only log to
info if logger exists.

This wasn't caught earlier because these tests only run after a merge.

actionpack/lib/action_controller/metal/implicit_render.rb

@@ -10,7 +10,7 @@ module ActionController
       if template_exists?(action_name.to_s, _prefixes, variants: request.variant)
         render(*args)
       else
-        logger.info "No template found for #{self.class.name}\##{action_name}, rendering head :no_content"
+        logger.info "No template found for #{self.class.name}\##{action_name}, rendering head :no_content" if logger
         head :no_content
       end
     end

actionpack/test/controller/mime/respond_to_test.rb

@@ -1,4 +1,5 @@
 require 'abstract_unit'
+require "active_support/log_subscriber/test_helper"
 
 class RespondToController < ActionController::Base
   layout :set_layout