Remove engine_version ignore

Why this change is being made:
- We want to upgrade Redis for Hub. It's currently stuck on version 6
  and we want to be able to add a var to set the version
  [see terraform-flightdeck-aws-application](thoughtbot/terraform-flightdeck-aws-application#25)
  and use that for our Hub infrastructure [see
  infra](thoughtbot/thoughtbot-infra#268)

What were the changes made to support this:
- remove ignored engine_version

Author: brian-penguin

elasticache-redis/replication-group/main.tf

@@ -29,9 +29,7 @@ resource "aws_elasticache_replication_group" "this" {
   lifecycle {
     ignore_changes = [
       # The token should be rotated externally
-      auth_token,
-      # Minor upgrades will cause noise in diffs
-      engine_version
+      auth_token
     ]
   }
 }