Try bookworm

Signed-off-by: Marcel Müller <marcel-mueller@gmx.de>

shallow-server/Dockerfile

@@ -1,4 +1,4 @@
-FROM debian:bullseye
+FROM debian:bookworm
 
 # Update repos install packages and cleanup
 # all in one step so we avoid large intermediate layers.
@@ -17,10 +17,6 @@ RUN apt-get update && \
     apt-get autoremove -y && apt-get autoclean && apt-get clean && \
     rm -rf /tmp/* /var/tmp/* /var/lib/apt/lists/*
 
-# Use git version from bullseye-backports to work around an issue on self-hosted runner
-RUN echo "deb http://deb.debian.org/debian bullseye-backports main contrib non-free" >> /etc/apt/sources.list && \
-    apt-get update && apt-get -t bullseye-backports install git -y
-
 COPY opcache-recommended.ini /usr/local/etc/php/conf.d/
 
 WORKDIR /var/www/html