The previous backport of `mautrix-telegram`[1] appears to be a mistake
of mine (sorry for that!), unfortunately v0.9 isn't forward-compatible
due to a database migration, so this change can't be reversed.
The primary issue was that `telethon` was too old, so I decided to
upgrade it to 1.21 which is what I had on my 21.05-based tracking
branch while using `mautrix-telegram` anyways, so that's proven to work.
Closes#135583
[1] e1042038ac / cd84b8ad8b
Maximilian Bosch
4aa2488fd1