FIX: ensures `all_mentioned_user_ids` is not used as identifier (#21491)

A follow-up to 54b2a85b. That commit didn't fix the issue because the to_notify hash that we return from the notify_edit method isn't used anywhere apart from tests (that's confusing, we're going to fix that soon).

plugins/chat/lib/chat/notifier.rb

@@ -89,13 +89,14 @@ module Chat
           .pluck(:user_id)
 
       to_notify = list_users_to_notify
-      needs_notification_ids = to_notify[:all_mentioned_user_ids] - already_notified_user_ids
+      mentioned_user_ids = to_notify.extract!(:all_mentioned_user_ids)[:all_mentioned_user_ids]
+      needs_notification_ids = mentioned_user_ids - already_notified_user_ids
       return if needs_notification_ids.blank?
 
       notify_creator_of_inaccessible_mentions(to_notify)
       notify_mentioned_users(to_notify, already_notified_user_ids: already_notified_user_ids)
 
-      to_notify.except(:all_mentioned_user_ids)
+      to_notify
     end
 
     private

plugins/chat/spec/lib/chat/notifier_spec.rb

@@ -124,7 +124,8 @@ describe Chat::Notifier do
       describe "editing a direct mention into a global mention" do
         let(:mention) { "hello @#{user_2.username}!" }
 
-        it "doesn't return :all_mentioned_user_ids" do
+        it "doesn't send notifications with :all_mentioned_user_ids as an identifier" do
+          Jobs.run_immediately!
           msg = build_cooked_msg(mention, user_1)
 
           Chat::MessageUpdater.update(
@@ -133,8 +134,12 @@ describe Chat::Notifier do
             new_content: "hello @all",
           )
 
-          to_notify = described_class.new(msg, msg.created_at).notify_edit
-          expect(to_notify[:all_mentioned_user_ids]).not_to be_present
+          described_class.new(msg, msg.created_at).notify_edit
+
+          notifications = Notification.where(user: user_2)
+          notifications.each do |notification|
+            expect(notification.data).not_to include("\"identifier\":\"all_mentioned_user_ids\"")
+          end
         end
       end