Fix update bot /// was: Renew update bot token

The bot that creates an MR to update our PrivateStorageio-widely used nixpkgs version should have received a new GitLab token from the one of the last Terraform runs, but hasn't.

GitLab is mandatorily expiring tokens for a while now, with longest valid time a year (IIRC). We need to renew these tokens regularly.

Curiously, the bot that creates the weekly "Update production" MR is still going (see !532 (closed)), but the one that creates the "Update nixpkgs on develop" MR is not.