fix Docker image

fix Docker image

The Docker image is broken with the error message:

    scryer-prolog: error while loading shared libraries:
    libssl.so.1.1: cannot open shared object file: No such
    file or directory

We use the base base image `debian:stable-slim` and in the
background a new Debian version was marked stable (bookworm),
which has libssl3 instead of libssl1.1 installed.

I downgraded the base image to the previous stable version
(bullseye), which seems to fix the issue.