Upgrade base image from Debian Bullseye (oldstable) to Bookworm (stable)

Avail ourselves of newer (though still not _new_ ;) software, in
particular the SQLite CLI.

Dockerfile

@@ -224,7 +224,7 @@ RUN curl -fsSL https://ftp.ncbi.nlm.nih.gov/pub/datasets/command-line/v2/linux-$
 # This is in place for Python programs which are not easy to install for a
 # different target platform¹.
 # ¹ https://github.com/pypa/pip/issues/5453
-FROM --platform=$TARGETPLATFORM python:3.10-slim-bullseye AS builder-target-platform
+FROM --platform=$TARGETPLATFORM python:3.10-slim-bookworm AS builder-target-platform
 
 SHELL ["/bin/bash", "-e", "-u", "-o", "pipefail", "-c"]
 
@@ -350,7 +350,7 @@ RUN pip3 install evofr
 # ———————————————————————————————————————————————————————————————————— #
 
 # Now build the final image.
-FROM python:3.10-slim-bullseye AS final
+FROM python:3.10-slim-bookworm AS final
 
 SHELL ["/bin/bash", "-e", "-u", "-o", "pipefail", "-c"]