SinkBinding doesn't work with KServices that uses BYO revision names

**Describe the bug**

When using a `SinkBinding` with a Knative Service as subject that uses BYO revision names (i.e. setting the revision name from the client), then no `K_SINK` environment variable is injected to the KService.

**Expected behavior**

`K_SINK` should be injected to the Pod Template as a container env var regardless whether a Knative Service is configured for BYO revision names or not.

**To Reproduce**

```
kn service create random --image rhuss/random:1.0
kn broker create default
kn source binding create my-sb --subject Service:serving.knative.dev/v1:random --sink broker:default
kn service describe random --verbose | grep K_SINK
```
This will get no result as `kn` used BYO revision names by default. If switching over to server side generated names, then a K_SINK env var is injected.

```
# Switch over to server side generated names
kn service update random --revision-name ""
kn service describe random --verbose | grep K_SINK

Env: K_SINK=http://broker-ingress.knative-eventing.svc.cluster.local/default/default
```

**Knative release version**

Eventing 0.17.3 (running on minikube)

Start by reproducing the issue with the provided kn service, broker, and source binding commands, comparing BYO revision names with server-side generated names. Trace SinkBinding handling for the KService Pod Template and verify that K_SINK is injected in both configurations.

Written by the indexing model from the issue text.