chore(deps): Update ghcr.io/cloudnative-pg/postgresql Docker tag to v16.15

apps/wave-0/semaphore-db.yaml

@@ -49,7 +49,7 @@ spec:
   # Scaling out is non-disruptive: CNPG creates -2 then -3 sequentially, each seeded by
   # pg_basebackup from the running primary, which is neither restarted nor disconnected.
   instances: 3
-  imageName: ghcr.io/cloudnative-pg/postgresql:16.4
+  imageName: ghcr.io/cloudnative-pg/postgresql:16.15
   # Stamp app.kubernetes.io/name=semaphore-db onto every generated pod/service so the rendered
   # semaphore egress CiliumNetworkPolicy's toEndpoints selector matches the primary pod (R-NET-02).
   inheritedMetadata: