Correct data source name.

Author: ewbankkit

.changelog/#####.txt

@@ -1,3 +1,3 @@
 ```release-note:note
-data-source/aws_kms_key: This data source will be removed in a future version
+data-source/aws_kms_secret: This data source will be removed in a future version
 ```

website/docs/guides/version-6-upgrade.html.markdown

@@ -32,7 +32,7 @@ Upgrade topics:
 - [Data Source `aws_globalaccelerator_accelerator`](#data-source-aws_globalaccelerator_accelerator)
 - [Data Source `aws_identitystore_group`](#data-source-aws_identitystore_group)
 - [Data Source `aws_identitystore_user`](#data-source-aws_identitystore_user)
-- [Data Source `aws_kms_key`](#data-source-aws_kms_key)
+- [Data Source `aws_kms_secret`](#data-source-aws_kms_secret)
 - [Data Source `aws_launch_template`](#data-source-aws_launch_template)
 - [Data Source `aws_opensearch_domain`](#data-source-aws_opensearch_domain)
 - [Data Source `aws_opensearchserverless_security_config`](#data-source-aws_opensearchserverless_security_config)
@@ -370,7 +370,7 @@ To locate a user, update your configuration to use `alternate_identifier` instea
 
 ---
 
-## Data Source `aws_kms_key`
+## Data Source `aws_kms_secret`
 
 The functionality for this data source was removed in **v2.0.0** and the data source will be removed in a future version.