Grafana OCI artifact not being collected through oci tests

General MR

Summary

tests/oci-values.yaml contains overrides to use helmRepo instead of git. This was not updated recently after Grafana was moved out of the Monitoring chart to its own, leading to it still populating a GitRepository while the other packages correctly download HelmChart images from Registry1's OCI Repository

Relevant logs/screenshots

Installing bigbang using tests/oci-values.yaml will cause Grafana entries under kubectl get gitrepositories -n flux-system rather than kubectl get helmrepositories -n flux-system. This can further be validated by exec'ing in to the source controller and looking under the data folder.