Add PR 2600 to pending change log
Updates the pending change log with PR
### SDK Features
### SDK Enhancements
+* Add raw error message bytes to SerializationError errors ([#2600](https://github.com/aws/aws-sdk-go/pull/2600))
+ * Updates the SDK's API error message SerializationError handling to capture the original error message byte, and include it in the SerializationError error value.
+ * Fixes [#2562](https://github.com/aws/aws-sdk-go/issues/2562), [#2411](https://github.com/aws/aws-sdk-go/issues/2411), [#2315](https://github.com/aws/aws-sdk-go/issues/2315)
### SDK Bugs
