Build `.deb`s in CI

[samcday]

In #67 Debian's packaging was pulled upstream, primarily to facilitate building phrog in Phosh's nightly repo. But since the packaging is here, it'd be nice to be able to build .debs in PRs, and maybe even as release artifacts (even though folks should be preferring the properly packaged variant, of course).

I already yeeted out some YAMLs to make this so, problem is it doesn't work, for really stupid reasons that 13th February Sam doesn't want to think about. Tomorrow Sam or Next Week Sam might be more receptive, though.