APIServerSource EventTypes created once per namespace, not per source

**Describe the bug**
When there are more than one APIServerSource deployed to the same namespace, it seems like the eventtypes which are created by the duck reconciler only show up for one of the sources.

**Expected behavior**
Each APIServerSource should create 3 eventtypes, regardless of whether or not there already is an APIServerSource in the same namespace

**To Reproduce**
To reproduce, run:
```
SYSTEM_NAMESPACE=knative-eventing go test -v -count=1 -tags=e2e -run ApiServerSourceDataPlane_SinkTypes -timeout=8m ./test/rekt
```

This test creates three APIServerSources in one namespace, so you would expect to get 9 eventtypes created (each source creates 3). However, only one set of eventtypes is created.

**Knative release version**

**Additional context**
Add any other context about the problem here such as proposed priority

Start by running ./test/rekt with -run ApiServerSourceDataPlane_SinkTypes and inspect the APIServerSource and duck reconciler paths exercised by that test. Done means three APIServerSources in one namespace produce nine eventtypes, with three eventtypes for each source.

Written by the indexing model from the issue text.