One job, declared as [ci.NAME]. The header names it; runners names the
machines from [runners] it runs on, one check each. No os/arch/
triple: validation runs a machine’s checks, it does not cross-compile.
One machine, declared once as [runners.NAME]. The header names it; this
is how GitHub finds it. Every label is required at once, so a three-label
runner is one machine carrying three labels, not three machines.