cleanup: remove skip-on-latest in TestCacheWithExternalEtcdAndRootShard when kcp 0.31 is out

[gman0]

There is a temporary hack in test/e2e/cacheserver/cacheserver_test.go that skips the TestCacheWithExternalEtcdAndRootShard test with latest kcp.

Once kcp 0.31 is out, we need to remove that hack.

Details:

kcp-operator/test/e2e/cacheserver/cacheserver_test.go

Lines 96 to 103 in 96aafa1

	func TestCacheWithExternalEtcdAndRootShard(t *testing.T) {
	switch utils.GetKcpRelease() {
	// We skip release "" because it currently points to kcp 0.30 which
	// doesn't currently support cache-server with an external etcd cluster.
	case "release-0.28", "release-0.29", "release-30", "": // TODO(gman0): remove the empty ("") kcp release!
	t.Skip("running external etcd with cache-server is only supported with kcp >=0.31")
	return
	}

Note the "" check. An empty release means "latest kcp tag", i.e. 0.30 at the time of writing this ticket.

This KCP_RELEASE is set in:

• hack/ci/run-e2e-tests.sh
  

  kcp-operator/hack/ci/run-e2e-tests.sh

  Lines 22 to 25 in 96aafa1

  	# KCP_TAG (when coming from .prow.yaml) is set to release-* branch name.
  	# We stash it into KCP_RELEASE because KCP_TAG is overridden later to a specific
  	# git hash of that branch.
  	export KCP_RELEASE="${KCP_TAG:-}"

• The prow job pull-kcp-operator-test-e2e-default omits setting KCP_TAG, meaning the tag is empty, and so is the kcp image tag is defaults to latest.

Because TestCacheWithExternalEtcdAndRootShard relies on functionality that will be available only in >=0.31, we need to skip the test.

Once 0.31 is the latest, we should enable it.