Affected: Go: github.com/kyverno/kyverno

### Summary

Due to a missing error propagation in function `GetNamespaceSelectorsFromNamespaceLister` in `pkg/utils/engine/labels.go` it may happen that policy rules using namespace selector(s) in their `match` statements are mistakenly not applied during admission review request processing. As a consequence, security-critical mutations and validations are bypassed, potentially allowing attackers with K8s API access to perform malicious operations.

### Details

As a policy engine Kyverno is a critical component ensuring the security of Kubernetes clusters by apply security-relevant policy rules in the Kubernetes admission control process.

We encountered a case where Kyverno did not apply policy rules which should have been applied. This happened in both the mutation and the validation phase of admission control. Effectively Kyverno handled the admission review requests as if those policy rules did not exist. Consequently, the Kube API request was accepted without applying security-relevant patches and validations.

As the root cause we identified a missing error propagation in function `GetNamespaceSelectorsFromNamespaceLister` in `pkg/utils/engine/labels.go` ([src][1]).

All affected policy rules use a namespace selector in their match resource filters like this:

```yaml match: all: - resources: namespaceSelector: matchExpressions: - key: label1 operator: Exists ```

Such specification intents to apply rules only to resource object…