Describe the bug
Operator installs the knative operand, but it does not run the upgrade and downgrade tests available for knative.

Expected behavior
In the upgrade prow job, we need to add the upgrade and downgrade tests, verifying the knative serving.

To Reproduce
Steps to reproduce the behavior.
Submit a PR. Upgrade prow job is kicked off.

Knative release version
HEAD

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