This is going to happen. The best way to handle this inevitable occurrence is to ticket this. The reviewer should ask for the ticket, and have the ticket linked. The ticket should ready to go, and the author of the code should have it ready to go as the "next thing" to get done, whether that's the follow up, or it's getting picked up in the next sprint so it doesn't get missed.

The code reviewer should also watch that ticket, and be prepared to assist it pushing it through.

If you just leave the task in the code, it will get lost. And, on occasion, the pressure of needing to write a ticket will get someone to just make the fix instead of having to create the ticket.