Use trafficmanager.net

Signed-off-by: René Jochum <rene@jochum.dev>

Dockerfile

@@ -3,6 +3,7 @@ FROM registry.jochum.dev/library/debian:buster-slim
 LABEL maintainer "René Jochum <rene@jochum.dev>"
 
 RUN set -ex; \
+    sed -i 's/deb.debian.org/debian-archive.trafficmanager.net/g' /etc/apt/sources.list && \
     apt-get update --allow-releaseinfo-change && \
     apt-get install --no-install-recommends -y -o 'DPkg::Options::=--force-confold' -o 'DPkg::Options::=--force-confdef' gnupg apt-transport-https curl ca-certificates && \
     curl https://repo.dovecot.org/DOVECOT-REPO-GPG | gpg --import && \