prow.sh: use csi-test v4.2.0

The recently added -csi.checkpathcmd and the associated test are
supported only by csi-test v4.2.0.

prow.sh

@@ -239,7 +239,7 @@ configvar CSI_PROW_E2E_IMPORT_PATH "k8s.io/kubernetes" "E2E package"
 # of the cluster. The alternative would have been to (cross-)compile csi-sanity
 # and install it inside the cluster, which is not necessarily easier.
 configvar CSI_PROW_SANITY_REPO https://github.com/kubernetes-csi/csi-test "csi-test repo"
-configvar CSI_PROW_SANITY_VERSION v4.0.2 "csi-test version" # v4.0.2
+configvar CSI_PROW_SANITY_VERSION v4.2.0 "csi-test version"
 configvar CSI_PROW_SANITY_PACKAGE_PATH github.com/kubernetes-csi/csi-test "csi-test package"
 configvar CSI_PROW_SANITY_SERVICE "hostpath-service" "Kubernetes TCP service name that exposes csi.sock"
 configvar CSI_PROW_SANITY_POD "csi-hostpathplugin-0" "Kubernetes pod with CSI driver"