re-enable nodepool upgrade test (Replace only)

In PR https://github.com/openshift/hypershift/pull/2576/ we had to disable the nodepool upgrade test. This is because there are no previous releases which have the new kubevirt rhcos variant available... so there's no release to upgrade from

We need to re-enable this test once we have a stable previously release in CI to test against (post 4.14 feature freeze and after 4.15 is branched.)