FIX: Correct assign user autocomplete logic

Previously we were only autocompleting users which were in the same group as the acting user.

app/controllers/discourse_assign/assign_controller.rb

@@ -24,7 +24,7 @@ module DiscourseAssign
         .limit(6)
 
       render json: {
-        assign_allowed_on_groups: current_user.visible_groups.assign_allowed_groups.pluck(:name),
+        assign_allowed_on_groups: Group.visible_groups(current_user).assign_allowed_groups.pluck(:name),
         suggestions: ActiveModel::ArraySerializer.new(users, scope: guardian, each_serializer: BasicUserSerializer)
       }
     end

assets/javascripts/discourse/templates/modal/assign-user.hbs

@@ -4,7 +4,6 @@
   {{user-selector
       single=true
       allowAny=false
-      group="staff"
       groupMembersOf=allowedGroups
       excludeCurrentUser=false
       includeMentionableGroups=false

spec/requests/assign_controller_spec.rb

@@ -11,6 +11,7 @@ RSpec.describe DiscourseAssign::AssignController do
   let(:user) { Fabricate(:admin, groups: [default_allowed_group]) }
   let(:post) { Fabricate(:post) }
   let(:user2) { Fabricate(:active_user) }
+  let(:nonadmin) { Fabricate(:user, groups: [default_allowed_group]) }
 
   describe 'only allow users from allowed groups' do
     before { sign_in(user2) }
@@ -56,9 +57,11 @@ RSpec.describe DiscourseAssign::AssignController do
       end
 
       it 'does include only visible assign_allowed_on_groups' do
-        visible_group = Fabricate(:group, members_visibility_level: Group.visibility_levels[:members])
-        visible_group.add(user)
-        invisible_group = Fabricate(:group, members_visibility_level: Group.visibility_levels[:members])
+        sign_in(nonadmin) # Need to use nonadmin to test. Admins can see all groups
+
+        visible_group = Fabricate(:group, visibility_level: Group.visibility_levels[:members])
+        visible_group.add(nonadmin)
+        invisible_group = Fabricate(:group, visibility_level: Group.visibility_levels[:members])
 
         SiteSetting.assign_allowed_on_groups = "#{visible_group.id}|#{invisible_group.id}"