This is to add an initial step for the CI so that, hopefully, it will
cache deps and next step (docs and tests) will be faster.

This one seems to work with nix builds.

One issue is that it creates new list/docs/board/graph nodes.

Database.PostgreSQL.Simple.Time.Printer.year:  years BCE not supportedCallStack (from HasCallStack):  error, called at src/Database/PostgreSQL/Simple/Time/Internal/Printer.hs:83:23 in postgresql-simple-0.6.4-JK0smXwdTUMDl7m3Ne57PV:Database.PostgreSQL.Simple.Time.Internal.Printer