chore: CIDR format for allowed admin IPs (#265)

Avoid terraform changes while remaining correct for the storage account
(cf
https://github.com/jenkins-infra/azure/pull/264#issuecomment-1401712541)

privatek8s.tf

@@ -31,7 +31,7 @@ resource "azurerm_kubernetes_cluster" "privatek8s" {
 
   api_server_access_profile {
     authorized_ip_ranges = setunion(
-      values(local.admin_allowed_ips),
+      formatlist("%s/32", values(local.admin_allowed_ips)),
       data.azurerm_subnet.private_vnet_data_tier.address_prefixes,
     )
   }