Fix ungraded_discussion_student_visibilities scope when provided ids

refs LF-1051
flag=differentiated_modules

Test Plan
1. Turn on differentiated_modules flag for all tests
2. content_tag specs should pass

Change-Id: I69ef3266c38af81e216acf7518cddcf3c87d75cd
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/349001
Tested-by: Service Cloud Jenkins <[email protected]>
Reviewed-by: Robin Kuss <[email protected]>
QA-Review: Robin Kuss <[email protected]>
Product-Review: Jason Gillett <[email protected]>

Author: jasonxris

app/models/discussion_topic.rb

@@ -857,7 +857,7 @@ def initialize(message = nil, status_code = nil)
       if !course.nil? && course.is_a?(Course) && course.user_has_been_observer?(student)
         observed_student_ids = ObserverEnrollment.observed_student_ids(course, student)
       end
-      user_ids = [student.id].concat(observed_student_ids)
+      user_ids = Array(student).concat(observed_student_ids)
       visible_topic_ids = UngradedDiscussionVisibility::UngradedDiscussionVisibilityService.discussion_topics_visible_to_students_by_topics(user_ids:, discussion_topic_ids: ids).map(&:discussion_topic_id)
 
       merge(