Add 0.28.4 changelog notes for STS/SNS topic ARN resolution and types-aiobotocore sts typing

Author: kalaspuff

CHANGELOG.md

@@ -1,8 +1,9 @@
 # Changes
 
-## 0.28.4 (2025-xx-xx)
+## 0.28.4 (2026-xx-xx)
 
-- ...
+- When publishing to SNS, the AWS SNS+SQS transport resolves the topic ARN using `sts:GetCallerIdentity` (to obtain the AWS account ID) and `sns:GetTopicAttributes` on the constructed topic ARN before falling back to `sns:CreateTopic`. This supports deployments where the service is not allowed to call `sns:CreateTopic` but can publish to an existing topic with the usual AWS STS and AWS SNS read permissions.
+- Extended the `types-aiobotocore` dev dependency with the `sts` extra so STS clients are typed alongside SNS and SQS during development.
 
 ## 0.28.3 (2025-03-11)