ci: wait for DNS recovery after uninstall on Linux

systemd-resolved needs a moment to restore its stub listener after
the numa drop-in is removed. Without a wait, the runner can't resolve
GitHub's API to report job completion.

.github/workflows/ci.yml

@@ -93,6 +93,10 @@ jobs:
           sudo ./target/release/numa uninstall
           sleep 1
           ! curl -sf http://127.0.0.1:5380/health 2>/dev/null
+          # Wait for systemd-resolved to restore DNS so the runner can
+          # phone home to GitHub after the job completes.
+          sleep 3
+          dig @127.0.0.1 github.com +short +timeout=5 || dig github.com +short +timeout=5 || true
       - name: cleanup
         if: always()
         run: sudo ./target/release/numa uninstall 2>/dev/null || true