I have never heard the verb 'digress,' used in the passive voice. It sounds completely wrong. The verb is used in the active voice only, I believe. For example:
'The ballet, Firebird, by Igor Stravinsky was banned in Moscow. By the way censorship has a very long history with the first recorded instance having been in xxx bc. But, I digress, as I was saying about Firebird...'
We would simply say 'You have gone off topic.'