codeowners: change ownership of /data/ (#1210)

Author: gabor

.github/CODEOWNERS

@@ -3,5 +3,5 @@
 # these will be requested for review when someone opens a pull request.
 * @grafana/plugins-platform-backend
 /backend/gtime @grafana/observability-metrics @grafana/observability-logs @grafana/partner-datasources
-/data/ @grafana/data-plane-wg
+/data/ @grafana/grafana-datasources-core-services
 /data/sqlutil @grafana/oss-big-tent