fix(actions): reject jobs without runs-on (#39480)

Align job and `runs-on` validation with github.com, as implemented by
the parser in https://github.com/actions/runner. A job without `runs-on`
could be claimed by any runner, so a job meant for a container could run
on the host.

- Jobs without `runs-on` fail with `Required property is missing:
runs-on`, called workflows included
- Unknown job keys and callers (`uses:`) mixed with steps-only keys like
`runs-on` are rejected
- Empty, null and nested `runs-on` values are rejected
- A `runs-on` evaluating to such a value fails only that job
- Called workflows are validated at run creation, an invalid one fails
the run as an invalid workflow file
- Zero labels (`runs-on: []` or `{}`) never match a runner, including
jobs queued before upgrading

<img width="960" alt="image"
src="https://github.com/user-attachments/assets/e746ce5a-b711-4e8b-aab8-81336ff53d86"
/>

**Behavior Change:** workflows that omit `runs-on`, use unknown job keys
or mix `uses` with `runs-on` stop running until fixed.

---------

Co-authored-by: bircni <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>

routers/web/repo/actions/actions.go

@@ -569,7 +569,7 @@ func (data *actionRunListData) processActionRuns(ctx *context.Context) bool {
 					break
 				}
 			}
-			if job.Status.IsWaiting() {
+			if job.Status.IsWaiting() && !job.IsReusableCaller {
 				hasOnlineRunner := false
 				for _, runner := range runners {
 					if !runner.IsDisabled && runner.CanMatchLabels(job.RunsOn) {

routers/web/repo/actions/view.go

@@ -773,7 +773,7 @@ func describePendingJobDetail(ctx *context_module.Context, current *actions_mode
 		if pending := pendingNeeds(current, jobs); len(pending) > 0 {
 			return ctx.Locale.TrString("actions.runs.waiting_for_dependent_jobs", strings.Join(pending, ", "))
 		}
-	case current.Status.IsWaiting():
+	case current.Status.IsWaiting() && !current.IsReusableCaller: // a caller waits on its called jobs, never on a runner
 		// A waiting job has no runner to pick it up yet. A busy runner is still
 		// "online", so distinguish three cases: no runner online at all, online
 		// runners but none match the labels, and a matching runner that is busy.