[SuperTuxKart] Wrong reference to Debian version

**Egg:** SuperTuxKart
**File:** SuperTuxKart/egg-super-tux-kart.json

**Issue Description:**

Install script is referencing http://deb.debian.org/debian bullseye-backports

Should reference bookworm instead since ghcr.io/ptero-eggs/yolks:debian is bookworm