release branch: downgrade testing to v1beta1 API

Author: pohly

.prow.sh

@@ -3,7 +3,13 @@
 # This is specific to the release-2.1 branch and overrides the
 # version set in the prow config.
 export CSI_SNAPSHOTTER_VERSION=v2.1.2
+
+# The problem that this solves is that the prow config assumes
+# that Kubernetes 1.20 uses the v1 snapshotter API, whereas this
+# branch still uses v1beta1. By downgrading to an older deployment
+# and e2e.test suite we get tests to run.
 export CSI_PROW_DRIVER_VERSION=v1.4.0
+export CSI_PROW_E2E_VERSION=v1.19.7
 
 . release-tools/prow.sh