chore: use python-samples-reviewers (#659)

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

@@ -1,3 +1,3 @@
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-python:latest
-  digest: sha256:2f90537dd7df70f6b663cd654b1fa5dee483cf6a4edcfd46072b2775be8a23ec
+  digest: sha256:899d5d7cc340fa8ef9d8ae1a8cfba362c6898584f779e156f25ee828ba824610

.github/CODEOWNERS

@@ -8,5 +8,5 @@
 # @googleapis/yoshi-python @googleapis/api-spanner-python are the default owners for changes in this repo
 *     @googleapis/yoshi-python @googleapis/api-spanner-python
 
-# @googleapis/python-samples-owners @googleapis/api-spanner-python are the default owners for samples changes
-/samples/   @googleapis/python-samples-owners @googleapis/api-spanner-python
+# @googleapis/python-samples-reviewers @googleapis/api-spanner-python are the default owners for samples changes
+/samples/   @googleapis/python-samples-reviewers @googleapis/api-spanner-python