Update .changelog/28847.txt

Co-authored-by: Kit Ewbank <[email protected]>

.changelog/28847.txt

@@ -1,3 +1,3 @@
 ```release-note:bug
-resource/aws_db_instance: When changing to gp3 larger than allocated storage threshold, fix bug causing error `InvalidParameterCombination: You must specify both the storage size and iops when modifying the storage size or iops on a DB instance that has iops`
+resource/aws_db_instance: When changing a `gp3` volume's `allocated_storage` to a value larger than the [threshold value for `engine`](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_Storage.html#gp3-storage), fix bug causing error `InvalidParameterCombination: You must specify both the storage size and iops when modifying the storage size or iops on a DB instance that has iops`
 ```