ci: add silvermetal-builder checkout smoke (mirror clone auth repro)

.gitea/workflows/silvermetal-runner-smoke.yml

@@ -0,0 +1,14 @@
+name: silvermetal-runner-checkout-smoke
+on:
+  workflow_dispatch:
+
+jobs:
+  checkout-smoke:
+    runs-on: silvermetal-builder
+    steps:
+      - uses: actions/checkout@v4
+      - name: Prove checkout worked
+        run: |
+          echo "checkout OK"
+          ls -la
+          git log -1 --oneline