Use SchemeGroupVersion for tekton objects in cluster resolver
Use SchemeGroupVersion for tekton objects in cluster resolver

Prior, the cluster resolver sets the APIVersion of the retrieved tekton object
to be a fixed string "tekton.dev/v1beta1".

Now, we changed this to `v1beta1.SchemeGroupVersion.String()` for easier
transition to v1 once v1 is released.

Signed-off-by: Chuang Wang <5161cce741fb1626e53fe819fa9eba1da871a86c@google.com>

tektoncd/pipeline,tektoncd/pipeline