Work out how to test mixed-version chutney networks in Tor's CI

We need multiple tor versions to run a mixed network with Chutney.

I don't think we can install multiple tor versions in Chutney's CI, because we're using a package manager.

Maybe we could compile Tor in Tor's CI, and install the stable-release version of Tor?

We'd have to set up the tor-stable symlink for the test, too.