mkosi commit the issue has been seen with

main

Used host distribution

Debian Testing

Used target distribution

Debian 12 Bookworm

Linux kernel version used

No response

CPU architectures issue was seen on

None

Unexpected behaviour you saw

In my configuration apt is not installed on base image, but it will be installed on main image.

The following check, prevent APT sources file being installed to final image. It was introduced in 74eea36. (#3582)

if "apt" in itertools.chain(context.config.packages, context.config.volatile_packages):