upgrading.dbk: Suggest https not http in apt line

This was the only place i could find with http instead of https - perhaps this means that https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1003245 can be closed after this as well?

added 15 commits

• 8c90f946...d6993dc1 - 14 commits from branch ddp-team:master
• 6d1b04d0 - upgrading.dbk: Suggest https not http in apt line

Compare with previous version

enabled an automatic merge when the pipeline for 6d1b04d0 succeeds

merged