As controller runtime has deprecated and removed the webhook.Validator interface.

Issue discussing deprecation: kubernetes-sigs/controller-runtime#2596

Deprecation PR: kubernetes-sigs/controller-runtime#2639

Removal PR: kubernetes-sigs/controller-runtime#2877

Keda still uses the webhook.Validator interfaces
https://github.com/search?q=repo%3Akedacore%2Fkeda%20webhook.Validator&type=code

This prevents any downstream codebases attempting to upgrade to v0.20+ from importing the keda apis as the build throws the following error.

/api/v1alpha1/type_webhook.go:40:15: undefined: webhook.Validator