Add missing editor required by a boskos resource
1. Make the following accounts editors of the project:
* `knative-productivity-admins@googlegroups.com`
+ * `knative-tests@appspot.gserviceaccount.com`
* `prow-job@knative-tests.iam.gserviceaccount.com`
* `prow-job@knative-nightly.iam.gserviceaccount.com`
* `prow-job@knative-releases.iam.gserviceaccount.com`
