Update CHANGELOG.md for #33660

CHANGELOG.md

@@ -1,7 +1,14 @@
 ## 5.19.0 (Unreleased)
 
+BREAKING CHANGES:
+
+* data-source/aws_s3_bucket_object: Following migration to [AWS SDK for Go v2](https://aws.github.io/aws-sdk-go-v2/), the `metadata` attribute's [keys](https://developer.hashicorp.com/terraform/language/expressions/types#maps-objects) are always [returned in lowercase](https://pkg.go.dev/github.com/aws/aws-sdk-go-v2/service/s3#HeadObjectOutput) ([#33660](https://github.com/hashicorp/terraform-provider-aws/issues/33660))
+* data-source/aws_s3_object: Following migration to [AWS SDK for Go v2](https://aws.github.io/aws-sdk-go-v2/), the `metadata` attribute's [keys](https://developer.hashicorp.com/terraform/language/expressions/types#maps-objects) are always [returned in lowercase](https://pkg.go.dev/github.com/aws/aws-sdk-go-v2/service/s3#HeadObjectOutput) ([#33660](https://github.com/hashicorp/terraform-provider-aws/issues/33660))
+
 NOTES:
 
+* data-source/aws_s3_bucket_object: The `metadata` attribute's keys are now always returned in lowercase. Please modify configurations as necessary ([#33660](https://github.com/hashicorp/terraform-provider-aws/issues/33660))
+* data-source/aws_s3_object: The `metadata` attribute's keys are now always returned in lowercase. Please modify configurations as necessary ([#33660](https://github.com/hashicorp/terraform-provider-aws/issues/33660))
 * resource/aws_iam_*: This release introduces additional validation of IAM policy JSON arguments to detect duplicate keys. Previously, arguments with duplicated keys resulted in all but one of the key values being overwritten. Since this results in unexpected IAM policies being submitted to AWS, we have updated the validation logic to error in these cases. This may cause existing IAM policy arguments to fail validation, however, those policies are likely not what was originally intended. ([#33570](https://github.com/hashicorp/terraform-provider-aws/issues/33570))
 
 FEATURES: