chore: pin version in simple_regional_with_ipv6 example (#2115)

Author: wyardley

examples/simple_regional_with_ipv6/main.tf

@@ -27,7 +27,9 @@ provider "kubernetes" {
 }
 
 module "gke" {
-  source                 = "terraform-google-modules/kubernetes-engine/google"
+  source  = "terraform-google-modules/kubernetes-engine/google"
+  version = "~> 33.0"
+
   project_id             = var.project_id
   name                   = "${local.cluster_type}-cluster${var.cluster_name_suffix}"
   regional               = true