fix roleName & specify region as variable

[ShotaKitazawa]

Description

Fixes # (issue)

Type of change

• Document update or simple typo fix
• Maintenance/update components
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• I have checked backward/forward compatibility that may cause regarding this change.

[github-actions]

✅ Preview for stg

[github-actions]

✅ Preview for prod

--- arn:aws:ecs:ap-northeast-1:607167088920:task-definition/dreamkast-prod-seaman:24
+++ prod/seaman/task-def.jsonnet
@@ -90,7 +90,6 @@
   "taskRoleArn": "arn:aws:iam::607167088920:role/dreamkast-prod-ecs-seaman",
   "volumes": [
     {
-      "host": {},
       "name": "config"
     }
   ]