unread-ops: Add check to make mark_as_read_turned_off_banner visible.

When processing an "update_message_flags" event to mark messages
as unread, check the current message list once messages are updated
to see if the `mark_as_read_turned_off_banner` should be visible.

This means that other clients in a view that also does not mark
messages as read (for example a sender or keyword search narrow)
will also load the banner when the view is updated.

Fixes #23502.

static/js/unread_ops.js

@@ -159,6 +159,13 @@ export function process_unread_messages_event({message_ids, message_details}) {
     */
     message_live_update.rerender_messages_view();
 
+    if (
+        !message_lists.current.can_mark_messages_read() &&
+        message_lists.current.has_unread_messages()
+    ) {
+        unread_ui.notify_messages_remain_unread();
+    }
+
     unread_ui.update_unread_counts();
 }