[terraform] bump prod identity to 0.39

Summary:
should resolve some of the alarms we're getting on prod

haven't seen any regressions on staging since we deployed 0.39 there

Test Plan: terraform plan

Reviewers: bartek, will, ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13559

services/terraform/remote/service_identity.tf

@@ -1,5 +1,5 @@
 locals {
-  identity_service_image_tag      = local.is_staging ? "0.39" : "0.37"
+  identity_service_image_tag      = local.is_staging ? "0.39" : "0.39"
   identity_service_server_image   = "commapp/identity-server:${local.identity_service_image_tag}"
   identity_service_container_name = "identity-server"