simple sed oneliner to replace a repo (adds one thin layer of 1 changed debian.sources)
RUN sed -i -e 's|http://deb.debian.org/debian|http://mirror.yandex.ru/debian|g' /etc/apt/sources.list.d/debian.sources
# then proceed as usual:
RUN apt update && apt install -y --no-install-recommends your_packages_here && rm -rf /var/lib/apt/lists/*