Upgrade Weblate to 3.9+
Currently, Weblate is in 3.9 and we're running 3.5.
Upgrading is a time consuming task because:
- Some minor versions can't be skipped.
- New/old dependencies have to be checked an puppetized.
- Commands have to be run by hand to migrate tables, copy static files, and refresh configs.
- Migration problems may arise.
Despite that, it's better do it earlier (or frequently) than accumulate.