Control ssh binaries in CI #16
Description
There is at least one behavior difference between relatively modern and very recent ssh related to config parsing: #15 (comment) (Ports may, after a certain point, be given as named entries in the service database as Port ssh and not just as numeric Port 22).
Depending on the Github-provided ssh makes it impossible to test this behavior: we should discover how to override the system ssh (via docker or otherwise). Depending on what kinds of behavior differences we observe, we may want to run integration tests against multiple versions of ssh in the future.