Fix yunikorn-k8shim CI checks

[richscott]

The CI checks for the yunikorn-k8shim repo fail, due to incorrect registry values (for example, there is no github.com/G-Research/yunikorn-release repo to pull Helm charts from - we must use the apache/yunikorn-release repo, or fork our own, if needed). Also, the Spark integration test times-out.