Build backend images with bookworm

Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>

Dockerfile.backend

@@ -2,14 +2,14 @@
 ARG DEBIAN_FRONTEND=noninteractive
 ARG GOPATH=/usr/local/go
 
-FROM rust:1.70-bullseye as aptly-tools-builder
+FROM rust:1.70-bookworm as aptly-tools-builder
 RUN git clone https://github.com/collabora/aptly-rest-tools \
               -b v0.0.4 --depth=1 \
               /tmp/aptly-rest-tools
 WORKDIR /tmp/aptly-rest-tools
 RUN cargo build --release
 
-FROM debian:bullseye-slim as server
+FROM debian:bookworm-slim as server
 LABEL maintainer Andrej Shadura <andrew.shadura@collabora.co.uk>
 ENV LC_ALL=C.UTF-8
 ARG WORKDIR=/tmp/sources