Hi! the great news is that Georg Koppen and Nicolas Vigier from the Torproject have been very helpful and created a temporary fix for this situation. Nicolas even committed a pull request for torbrowser-launcher to use the new URL to check for updates (see https://github.com/micahflee/torbrowser-launcher/pull/279).
So thanks to them <333, this works again right now in torbrowser-launcher 0.2.7 and once Micah Lee, the upstream author, includes Nicolas' commit, we'll have this change in Debian, too. Cheers, Ulrike