Misleading error message when cohort has no parent and have borrowingLimit

[nasedil]

What happened:
When defining a cohort that has no parent cohort and has borrowingLimit the following error message is shown:

admission webhook "vcohort.kb.io" denied the request: spec.resourceGroups[0].flavors[0].resources[0].borrowingLimit: Invalid value: "0": must be nil when cohort is empty

The message is misleading because clusterQueue object has cohort field for its parent cohort while cohort object has parent field for it's parent cohort. And the error message is same for both cases.
What you expected to happen:
The message could end with must be nil when parent is empty ormust be nil when parent cohort is empty.
How to reproduce it (as minimally and precisely as possible):
Applying the following YAML file:

---
apiVersion: kueue.x-k8s.io/v1beta1
kind: ResourceFlavor
metadata:
  name: pod-performance-resource-flavor
---
apiVersion: kueue.x-k8s.io/v1alpha1
kind: Cohort
metadata:
  name: test-cohort
spec:
  # there is no parent cohort
  # parent: ~
  resourceGroups:
    - coveredResources: ["pods"]
      flavors:
        - name: "pod-performance-resource-flavor"
          resources:
            - name: "pods"
              nominalQuota: 1
              borrowingLimit: 0
...

Anything else we need to know?:

Environment:

• Kubernetes version (use kubectl version): v1.31.5
• Kueue version (use git describe --tags --dirty --always): v0.11.0-devel-244-gfd6a5206
• Cloud provider or hardware configuration: GCP GKE
• OS (e.g: cat /etc/os-release): Debian GNU/Linux
• Kernel (e.g. uname -a):
• Install tools:
• Others:

[nasedil]

/assign