chore: add spanner-team to CODEOWNERS (#16586)

add spanner-team to CODEOWNERS

Author: ohmayr

.github/CODEOWNERS

@@ -12,4 +12,6 @@
 *                                             @googleapis/cloud-sdk-python-team @googleapis/cloud-sdk-librarian-team
 
 /packages/bigframes/                          @googleapis/cloud-sdk-python-team @googleapis/cloud-sdk-librarian-team @googleapis/bigquery-dataframe-team
+/packages/django-google-spanner/              @googleapis/cloud-sdk-python-team @googleapis/cloud-sdk-librarian-team @googleapis/spanner-team
 /packages/google-auth/                        @googleapis/cloud-sdk-python-team @googleapis/cloud-sdk-librarian-team @googleapis/cloud-sdk-auth-team @googleapis/aion-team
+/packages/google-cloud-spanner/               @googleapis/cloud-sdk-python-team @googleapis/cloud-sdk-librarian-team @googleapis/spanner-team