Update CHANGELOG for #24744

CHANGELOG.md

@@ -17,7 +17,13 @@ BREAKING CHANGES:
 * The official MacOS builds of Terraform CLI are no longer compatible with Mac OS 10.10 Yosemite; Terraform now requires at least Mac OS 10.11 El Capitan. Terraform 0.13 is the last major release that will support 10.11 El Capitan, so if you are upgrading your OS we recommend upgrading to Mac OS 10.12 Sierra or later.
 * The official FreeBSD builds of Terraform CLI are no longer compatible with FreeBSD 10.x, which has reached end-of-life. Terraform now requires FreeBSD 11.2 or later.
 
+NOTES:
+
+* backend/s3: Region validation now automatically supports the new `af-south-1` (Africa (Cape Town)) region. For AWS operations to work in the new region, the region must be explicitly enabled as outlined in the [AWS Documentation](https://docs.aws.amazon.com/general/latest/gr/rande-manage.html#rande-manage-enable). When the region is not enabled, the Terraform S3 Backend will return errors during credential validation (e.g. `error validating provider credentials: error calling sts:GetCallerIdentity: InvalidClientTokenId: The security token included in the request is invalid`). [GH-24744]
+
 ENHANCEMENTS:
+
+* backend/s3: Support automatic region validation for `af-south-1` [GH-24744]
 * config: `templatefile` function will now return a helpful error message if a given variable has an invalid name, rather than relying on a syntax error in the template parsing itself. [GH-24184]
 * config: The configuration language now uses Unicode 12.0 character tables for certain Unicode-version-sensitive operations on strings, such as the `upper` and `lower` functions. Those working with strings containing new characters introduced since Unicode 9.0 may see small differences in behavior as a result of these table updates.
 * core: added support for passing metadata from modules to providers using HCL [GH-22583]