workload-cluster dependency on mgmt-cluster-ready isn't effective

for workload cluster sylva-units chart currently produces a broken manifest:

apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
  name: ...
spec: 
  components: []
  depends_on:  # <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
    mgmt-cluster-ready: true
  dependsOn:
  - name: cluster-machines-ready
  - name: cluster-reachable
  - name: namespace-defs

This is due to !1923 (merged) having made a wrong use of unit_kustomization_spec_default.

This inexisting depends_on field is silently ignored (unfortunate behavior of Helm...), making !1923 (merged) ineffective.