This was reported by a user on the [tor-relays mailing list](https://lists.torproject.org/mailman3/hyperkitty/list/tor-relays@lists.torproject.org/thread/FF5U7Y3IHXU6V3UYU4RTUFGJDHFKCJ4J/) The package `deb.torproject.org-keyring` is indeed absent from the archive for this suite/release.