chore: update spanner owners to group
/firestore/ @enocom @dmahugh @tritone @crwilcox @googleapis/yoshi-go-admins
/pubsub/ @googleapis/api-pubsub @googleapis/yoshi-go-admins
/pubsublite/ @googleapis/api-pubsub @googleapis/yoshi-go-admins
-/spanner/ @skuruppu @hengfengli @googleapis/yoshi-go-admins
+/spanner/ @googleapis/api-spanner-go @googleapis/yoshi-go-admins
/storage/ @googleapis/cloud-storage-dpe @googleapis/yoshi-go-admins
/errorreporting/ @googleapis/api-logging @googleapis/yoshi-go-admins
/logging/ @googleapis/api-logging @googleapis/yoshi-go-admins
