FIX: Publish membership update events when refreshing automatic groups. (#17668)

Adding or removing users from automatic groups is now consistent with `Group#add` and `Group#remove`.

spec/models/group_spec.rb

@@ -242,6 +242,41 @@ describe Group do
       expect(GroupUser.where(user_id: staged.id).count).to eq(2)
     end
 
+    describe 'after updating automatic group members' do
+      fab!(:user) { Fabricate(:user) }
+
+      it 'triggers an event when a user is removed from an automatic group' do
+        tl3_users = Group.find(Group::AUTO_GROUPS[:trust_level_3])
+        tl3_users.add(user)
+
+        events = DiscourseEvent.track_events do
+          Group.refresh_automatic_group!(:trust_level_3)
+        end
+
+        expect(GroupUser.exists?(group: tl3_users, user: user)).to eq(false)
+        publish_event_job_args = Jobs::PublishGroupMembershipUpdates.jobs.last['args'].first
+        expect(publish_event_job_args["user_ids"]).to include(user.id)
+        expect(publish_event_job_args["group_id"]).to eq(tl3_users.id)
+        expect(publish_event_job_args["type"]).to include('remove')
+      end
+
+      it 'triggers an event when a user is added to an automatic group' do
+        tl0_users = Group.find(Group::AUTO_GROUPS[:trust_level_0])
+
+        expect(GroupUser.exists?(group: tl0_users, user: user)).to eq(false)
+
+        events = DiscourseEvent.track_events do
+          Group.refresh_automatic_group!(:trust_level_0)
+        end
+
+        expect(GroupUser.exists?(group: tl0_users, user: user)).to eq(true)
+        publish_event_job_args = Jobs::PublishGroupMembershipUpdates.jobs.last['args'].first
+        expect(publish_event_job_args["user_ids"]).to include(user.id)
+        expect(publish_event_job_args["group_id"]).to eq(tl0_users.id)
+        expect(publish_event_job_args["type"]).to eq('add')
+      end
+    end
+
     it "makes sure the everyone group is not visible except to staff" do
       g = Group.refresh_automatic_group!(:everyone)
       expect(g.visibility_level).to eq(Group.visibility_levels[:staff])