Pull in readiness-checker image and re-enable helm tests.

When we upgraded to Kyverno v1.17.0, the helm tests started failing because they now have a dependency on a readiness-checker image that does not yet exist in registry1. We temporarily disabled the tests to ship v1.17.0, and requested that Iron Bank add the image.

When the image is available, we need to swap it in as the test image in values.yaml, and re-enable the tests.

Here is Iron Bank's issue tracking their work to add the new image: dsop/opensource/kyverno/kyverno/readiness-checker#7 (closed).

Initially opening this issue with the status::blocked label since we are waiting for the image.