fix apply-workload-cluster.sh, namespace not found

This fixes a regression introduced in !2751 (merged) (not catched before merge because it occurs only on workload clusters fresh installs and this MR was tested with ci-featuretest-upgrade-from-1.2.1):

📜 Install a sylva-units Helm release for workload cluster rke2-capm3-virt 00:00
⏸ Suspend sylva-units HelmRelease/HelmChart
Error from server (NotFound): namespaces "rke2-capm3-virt" not found