The workflow only ran on push, so a pull request opened from a fork
never got a build, and neither did the host-side unit tests that run in
the same job.
The harness builds with the gcc the workflow already installs and runs
in under a second, so it goes before the SDCC steps and fails the build
first when a host-visible regression lands.
PR #119 made that no machine-type is selected, so the build will fail.
commit 2f787fee enables us select a machine via a variable, use this to
select a machine-type `KP_9000_6XHML_X2` to build.