[skip ci] Add comment for uninstall_helm script (#11443)

Signed-off-by: NJenny Li <jing.li@zilliz.com>

tests/scripts/uninstall_milvus.sh

@@ -21,5 +21,7 @@ helm uninstall -n "${MILVUS_HELM_NAMESPACE}" "${MILVUS_HELM_RELEASE_NAME}"
 
 MILVUS_LABELS1="app.kubernetes.io/instance=${MILVUS_HELM_RELEASE_NAME}"
 MILVUS_LABELS2="release=${MILVUS_HELM_RELEASE_NAME}"
+
+# Clean up pvc
 kubectl delete pvc -n "${MILVUS_HELM_NAMESPACE}" $(kubectl get pvc -n "${MILVUS_HELM_NAMESPACE}" -l "${MILVUS_LABELS1}" -o jsonpath='{range.items[*]}{.metadata.name} ') || true
 kubectl delete pvc -n "${MILVUS_HELM_NAMESPACE}" $(kubectl get pvc -n "${MILVUS_HELM_NAMESPACE}" -l "${MILVUS_LABELS2}" -o jsonpath='{range.items[*]}{.metadata.name} ') || true