Constrain lintian work requests to run on a matching architecture

While strictly speaking lintian doesn't particularly need to run on an architecture matching the binaries (although we probably ought to install binutils-multiarch if we're running on a different one, which we don't at the moment), that leaves open the possibility that there might not be an environment for the target suite and architecture combination. Looking up environments is complex enough that we don't want to do it in can_run_on, so it seems simplest to just configure those work requests to run on an architecture matching the binaries.

Fixes: #866 (closed)