IAM: Retain region attribute within the Policy object

Author: viren-nadkarni

moto/iam/models.py

@@ -174,6 +174,7 @@ def __init__(
     ):
         self.name = name
         self.account_id = account_id
+        self.region = region
         self.attachment_count = 0
         self.description = description or ""
         self.id = random_policy_id()