Disable webhook for net-certmanager-webhook (#11315)
Disable webhook for net-certmanager-webhook (#11315)

This patch disables chaos duck for net-certmanager-webhook.

Although chaos duck for webhook and domainmapping-webhook is disabled,
net-certmanager-webhook is not disabled.

It seems TestRevisionGC is failing because setting config-gc failed by
webhook issue.

```
Setting config-gc to immediate garbage collectionError from server (InternalError): Internal error occurred: failed calling webhook "config.webhook.net-certmanager.networking.internal.knative.dev": Post https://net-certmanager-webhook.fa21803d-a9d6-4a0d-8740-2149102cce16.svc:443/config-validation?timeout=30s: no endpoints available for service "net-certmanager-webhook"
```

Related to https://github.com/knative/serving/issues/11307
knative/serving,knative/serving