enable sandbox-privileged-namespace unit (for `kubectl debug` commands)

In sylva-projects/sylva-core!2961 (merged), I plan to add this commit sylva-projects/sylva-core!3190 (16a165c7) which let debug-on-exit use kubectl debug node commands to run data collection commands on the cluster nodes.

For kubectl debug node to be run we need a privileged namespace, which this CI configuration is enabling.