use v1.28.8+k0s.0 as previous k0s version

Author: sgalsaleh

Makefile

@@ -27,7 +27,7 @@ VELERO_IMAGE_VERSION = v1.13.2
 VELERO_AWS_PLUGIN_IMAGE_VERSION = v1.9.2
 KUBECTL_VERSION = v1.28.9
 K0S_VERSION = v1.28.9+k0s.0
-PREVIOUS_K0S_VERSION ?= v1.27.13+k0s.0
+PREVIOUS_K0S_VERSION ?= v1.28.8+k0s.0
 K0S_BINARY_SOURCE_OVERRIDE =
 TROUBLESHOOT_VERSION = v0.88.1
 KOTS_VERSION = v$(shell echo $(ADMIN_CONSOLE_CHART_VERSION) | sed 's/\([0-9]\+\.[0-9]\+\.[0-9]\+\).*/\1/')