chore: update CODEOWNERS for spanner samples (#6671)
chore: update CODEOWNERS for spanner samples (#6671)

* chore: update CODEOWNERS for spanner samples

* chore: update to appropriate team for Spanner

Co-authored-by: Charles Engelke <2f8855ae1777b7825ea5c6a2e808e18e09aa7e61@google.com>
GoogleCloudPlatform/python-docs-samples,GoogleCloudPlatform/python-docs-samples,GoogleCloudPlatform/python-docs-samples,GoogleCloudPlatform/python-docs-samples