fix(k8s): support control-plane tests on slim runner

k8s/backup-k3s-control-plane-config.sh

@@ -238,6 +238,10 @@ add_archive_entry_if_present() {
     local relative_path
     local protected_path
 
+    if [[ "$absolute_path" =~ (^|/)(\.|\.\.)(/|$) ]]; then
+        die "Configured source path is not safe to archive"
+    fi
+
     if [[ ! -e "$absolute_path" && ! -L "$absolute_path" ]]; then
         return 0
     fi