FIX: Use Guardian.basic_user instead of new (anon) (#24705)

c.f. de983796e1b66aa2ab039a4fb6e32cec8a65a098

There will soon be additional login_required checks
for Guardian, and the intent of many checks by automated
systems is better fulfilled by using BasicUser, which
simulates a logged in TL0 forum user, rather than an
anon user.

In some cases the use of anon still makes sense (e.g.
anonymous_cache), and in that case the more explicit
`Guardian.anon_user` is used

plugins/poll/lib/polls_updater.rb

@@ -114,7 +114,7 @@ module DiscoursePoll
               polls,
               each_serializer: PollSerializer,
               root: false,
-              scope: Guardian.new(nil),
+              scope: Guardian.basic_user,
             ).as_json
           post.publish_message!("/polls/#{post.topic_id}", post_id: post.id, polls: polls)
         end