Fix notification broadcast test for turbo-rails 2.0.21

turbo-rails 2.0.21 changed `capture_turbo_stream_broadcasts` to only
return broadcasts produced within the block, matching its documented
behavior (see hotwired/turbo-rails#736).

Since `broadcast_unread` uses `broadcast_prepend_later_to` (async via
job), we need to wrap the call in `perform_enqueued_jobs` so the
broadcast actually happens within the assertion block.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

test/models/notification_test.rb

@@ -15,7 +15,9 @@ class NotificationTest < ActiveSupport::TestCase
     notification.read # Mark as read first
 
     assert_turbo_stream_broadcasts([ notification.user, :notifications ], count: 1) do
-      notification.unread
+      perform_enqueued_jobs do
+        notification.unread
+      end
     end
   end