Move eventtype rekt test for pingsource to experimental rekt tests

[Leo6Leo]

          > [#7165 (comment)](https://github.com/knative/eventing/issues/7165#issuecomment-1673479276)

As Knative documentation said, Support for automatic registration is not supported for PingSource.
Should we add the support for PingSource to have auto eventType creation? Or we will enable the broker-side eventType auto creation for PingSource's rekt test?

So for this ticket, any suggestions on what should we do next? Should we add the support for PingSource to have auto eventType creation? @creydr

I agree with @Cali0707 in https://github.com/knative/eventing/pull/7166/files#r1290583414. We should not enable experimental features at this place.
For this PR to fix this logic (as the current logic is wrong), I would move this test to the experimental tests and then (when we have the support for auto event type creation in the pingsource) move it to the regular suite back (IMO).
That way, we can reuse the eventtype.WaitForEventType() and eventtype.AssertPresent() in other tests with the correct logic.

Originally posted by @creydr in #7166 (comment)