App Engine permanently blocks insecure traffic with TLS version 1.1 and earlier

## Feature Feature App Engine permanently blocks insecure traffic with TLS version 1.1 and earlier. For `appspot.com` domains, this block occurs at the connection level. For custom domains, the connection might succeed, but the requests are blocked. For more information, see[Secure minimum TLS](https://cloud.google.com/appengine/docs/flexible/secure-minimum-tls).