Include link to Tails news in Upgrade error messages
In order for users solve problems like #18127 we need them to read the release notes. To help them do that, let's include a link to Tails news, stating that there might be a known issue preventing the upgrade. IMHO these upgrader errors fit to include this link:
- An error occured while updating the signing key
- Error while checking for upgrades
Both of these error messages already includes a link to: https://tails.boum.org/doc/upgrade/error/check/ . So the link to Tails news could be put there if we don't want it straight in the error message.