groups.yaml: add 1.20 Enhancements Shadows
groups.yaml: add 1.20 Enhancements Shadows

add shadows to release-team and release-team-shadows

kubernetes/k8s.io,kubernetes/k8s.io,thockin/k8s.io,kubernetes/k8s.io,thockin/k8s.io,thockin/k8s.io,kubernetes/k8s.io,thockin/k8s.io