Installing knative-serving yamls second time without deleting the knative-serving namespace doesn't populate the webhook certs.

## What version of Knative?

> 1.4.0

## Expected Behavior

This is what I am doing and happening right now:
1. Create a new NS
2. kubectl apply -f on {serving-crds.yaml, serving-core.yaml, net-istio.yaml}
3. Everything works fine
4. Now, do kubectl delete -f on serving-crds.yaml + serving-core.yaml + net-istio.yaml
5. Once everything is cleaned up, i do `kubectl apply -f again in these 3 yamls
6. Everything should work fine

## Actual Behavior
1. Create a new NS
2. kubectl apply -f on {serving-crds.yaml, serving-core.yaml, net-istio.yaml}
3. Everything works fine
4. Now, do kuebctl delete -f on serving-crds.yaml + serving-core.yaml + net-istio.yaml
5. Once everything is cleaned up, i do `kubectl apply -f again in these 3 yamls
6. But this time, webhooks won’t run as their certs are not populated

Without deleting the namespace completely, re-apply of knative-serving second time would fail as webhooks certs won't be populated.

## Steps to Reproduce the Problem
1. Create a new NS
2. kubectl apply -f on {serving-crds.yaml, serving-core.yaml, net-istio.yaml}
3. Everything works fine
4. Now, do kuebctl delete -f on serving-crds.yaml + serving-core.yaml + net-istio.yaml
5. Once everything is cleaned up, i do `kubectl apply -f again in these 3 yamls
6. But this time, webhooks won’t run as their certs are not populated

Reproduce the sequence with serving-crds.yaml, serving-core.yaml, and net-istio.yaml: apply them, delete them while retaining the namespace, then apply them again. Inspect the second installation's webhook certificate state and determine what prevents the certs from being populated; done means the re-apply succeeds and the webhooks run normally.

Written by the indexing model from the issue text.