Fix changelog, comment on validation

Author: YakDriver

.changelog/40639.txt

@@ -1,3 +1,3 @@
 ```release-note:bug
-data-source/aws_iam_policy_document: Reverts 40652 due to issues. See: 40639.
+data-source/aws_iam_policy_document: Reverts plan-time validation for `statement` `sid`
 ```

internal/service/iam/policy_document_data_source.go

@@ -143,6 +143,8 @@ func dataSourcePolicyDocument() *schema.Resource {
 							"principals":        principalsSchema(),
 							names.AttrResources: setOfStringSchema(),
 							"sid": {
+								// Because policy documents are widely used outside IAM, we don't enforce
+								// IAM validation rules requiring alphanumeric and no spaces.
 								Type:     schema.TypeString,
 								Optional: true,
 							},