fix save-suggestions issues

• 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: #15079 (closed)

Original created by @Hefee on 16301 (Redmine)