Update endpoints model

Author: AWS SDK for Go v2 automation user

codegen/smithy-aws-go-codegen/src/main/resources/software/amazon/smithy/aws/go/codegen/endpoints.json

@@ -16974,6 +16974,7 @@
           "ap-southeast-3" : { },
           "ap-southeast-4" : { },
           "ap-southeast-5" : { },
+          "ap-southeast-6" : { },
           "ap-southeast-7" : { },
           "ca-central-1" : {
             "variants" : [ {