Dogfood free fix (#15327)

This allows the image specified to also update the free deployment when
using the github action.

Author: rfairburn

infrastructure/dogfood/terraform/aws-tf-module/free.tf

@@ -53,7 +53,7 @@ module "free" {
     cluster_name = local.customer_free
   }
   fleet_config = {
-    image               = "fleetdm/fleet:v4.40.0"
+    image               = local.fleet_image
     family              = local.customer_free
     security_group_name = local.customer_free
     awslogs = {
@@ -130,4 +130,4 @@ module "migrations_free" {
   task_definition_revision = module.free.byo-db.byo-ecs.task_definition.revision
   subnets                  = module.free.byo-db.byo-ecs.service.network_configuration[0].subnets
   security_groups          = module.free.byo-db.byo-ecs.service.network_configuration[0].security_groups
-}
+}