Revert upgrade from bullseye to bookworm

- we are being bitten by this issue on the Sussex VM deployment: docker-library/python#837 (comment) (other deployments work fine, as far as I can tell)

- the issue seems to be that old versions of Docker use an old version of libseccomp, which means that some syscalls are blocked when executing linux containers on a linux host. This bites us on Sussex VM

- to fix, we need to upgrade the version of Docker installed on the ITS virtual machine, but only ITS can do this. So we will need assistance from them. Until then, we need to revert to bullseye.

Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3.11-slim-bookworm
+FROM python:3.11-slim-bullseye
 
 RUN apt-get update && apt-get install -qq -y build-essential gcc gfortran mariadb-client mysqltuner libssl-dev libjpeg-dev zlib1g-dev libglpk-dev glpk-utils coinor-cbc git pkg-config swig wget libcairo2-dev libmagic1 --no-install-recommends