chore: update Sentinel Forwarder TF module (#937)

Update the module to the latest version that uses an SSM parameter
to store the Sentinel auth credentials.

terragrunt/aws/alarms/sentinel_logging.tf

@@ -3,7 +3,7 @@ locals {
 }
 
 module "sentinel_forwarder" {
-  source            = "github.com/cds-snc/terraform-modules//sentinel_forwarder?ref=v9.2.7"
+  source            = "github.com/cds-snc/terraform-modules//sentinel_forwarder?ref=v9.3.7"
   function_name     = "sentinel-cloud-watch-forwarder"
   billing_tag_value = var.billing_code