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>

tests/integration/actions_invalid_workflow_test.go

@@ -33,7 +33,7 @@ func TestActionsInvalidWorkflowPush(t *testing.T) {
 			content    string
 			wantErrors []string
 		}{
-			{"expression", "on: push\nrun-name: '${{ github.ref'\njobs: {check: {if: unknown.x}}\n", []string{"Unrecognized named-value: 'unknown'", "unclosed expression"}},
+			{"expression", "on: push\nrun-name: '${{ github.ref'\njobs: {check: {runs-on: ubuntu-latest, if: unknown.x}}\n", []string{"Unrecognized named-value: 'unknown'", "unclosed expression"}},
 			{"trigger", "on:\njobs: {check: {runs-on: ubuntu-latest, steps: [{run: echo hello}]}}\n", []string{"invalid event"}},
 		} {
 			t.Run(testCase.name, func(t *testing.T) {