fix save-suggestions issues

Originally created by @hefee on #16301 (Redmine)

• our python script eats exceptions, that are raised by git - that should break the build.
• let’s follow non fast forward HEAD in ~weblate/repositories/vcs/tails/index

Feature Branch: https://salsa.debian.org/hefee/puppet-tails/tree/hefee/dev/translation-server

Parent Task: tails#15079 (closed)