Use explicit Kubernetes versions for integration tests

.github/kubernetes-versions.json

@@ -0,0 +1,7 @@
+{
+  "versions": [
+    "1.36.0",
+    "1.35.0",
+    "1.34.0"
+  ]
+}

README.md

@@ -18,6 +18,20 @@ For example, if the current release is `1.29.0`, we support the following:
 
 Older releases should work as well, but we do not test them automatically, and we may decide not to fix bugs related to older releases.
 
+Integration tests run against explicit Kubernetes versions defined in `.github/kubernetes-versions.json`.
+
+To update tested versions:
+1. Edit `.github/kubernetes-versions.json`
+2. Update to the 3 latest minor releases
+3. Commit and push
+
+Example:
+```json
+{
+  "versions": ["1.36.0", "1.35.0", "1.34.0"]
+}
+```
+
 ## Try It Out
 
 To test the CCM on a vanilla Kubernetes cluster, you can use `helpers/run-in-test-cluster`. This will create a small Kubernetes cluster at cloudscale.ch,

helpers/test-matrix

@@ -1,14 +1,13 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-# Make sure the k8test/helpers/release-set CLI is available
-source helpers/run-in-test-cluster
-ensure-k8test > /dev/null
+# Read explicit Kubernetes versions from config
+K8S_VERSIONS=$(jq -r '.versions' .github/kubernetes-versions.json)
 
 # Returns the matrix entry for the given index (1-n)
 function matrixentry {
   # Kubernetes releases
-  k8test/helpers/release-set --kubernetes=$(( 1 - $1 )) --limit kubernetes | jq -r '.kubernetes.version'
+  echo "$K8S_VERSIONS" | jq -r ".[$(( $1 - 1 ))]"
 
   # The the private subnet range
   echo "10.100.$1.0/24"