[ci/deb] Allow using an existing UID/GID for the CI user

ci/Debian.Dockerfile

@@ -5,14 +5,10 @@ ARG BASE_IMAGE=ubuntu:jammy
 FROM $BASE_IMAGE
 LABEL name=darling-build-image version=0.1.0
 ARG DEBIAN_FRONTEND="noninteractive"
-ARG CI_UID=1111
-ARG CI_GID=1111
 RUN cp /etc/apt/sources.list /etc/apt/sources.list.d/sources-src.list && sed -i 's|deb http|deb-src http|g' /etc/apt/sources.list.d/sources-src.list
 RUN apt-get -y update
 RUN apt-get -y install cmake clang bison flex libfuse-dev libudev-dev pkg-config libc6-dev-i386 gcc-multilib libcairo2-dev libgl1-mesa-dev libglu1-mesa-dev libtiff5-dev libfreetype6-dev git git-lfs libelf-dev libxml2-dev libegl1-mesa-dev libfontconfig1-dev libbsd-dev libxrandr-dev libxcursor-dev libgif-dev libavutil-dev libpulse-dev libavformat-dev libavcodec-dev libswresample-dev libdbus-1-dev libxkbfile-dev libssl-dev llvm-dev libvulkan-dev && apt clean -y
 RUN apt-get -y install lsb-release && apt clean -y
-RUN groupadd -g "${CI_GID}" ci
-RUN useradd -u "${CI_UID}" -g "${CI_GID}" -m ci
 RUN apt-get -y install devscripts equivs debhelper && apt clean -y
 COPY control /control
 RUN mk-build-deps -i -r -t "apt-get --no-install-recommends -y" /control && apt clean -y
@@ -35,7 +31,11 @@ RUN if [ "$(cmake --version | head -n 1 | cut -d ' ' -f 3 | awk '{print $1"\n3.2
 
 RUN apt-get install -y --only-upgrade clang cmake && apt clean -y
 
+ARG CI_UID=1111
+ARG CI_GID=1111
+RUN groupadd -g "${CI_GID}" ci || true
+RUN useradd -u "${CI_UID}" -g "${CI_GID}" -m ci || true
 RUN mkdir -p /ccache
 RUN mkdir -p /src/mnt
-RUN chown -R ci:ci /src
-USER ci
+RUN chown -R ${CI_UID}:${CI_GID} /src
+USER ${CI_UID}:${CI_GID}