当在为 HTTP/2 流设置优先级时，该流可能被标记为父流的依赖项。
当试图标记流并依赖于它自己时，将使用此错误码。
When setting the priority for an HTTP/2 stream, the stream may be marked as
a dependency for a parent stream. This error code is used when an attempt is
made to mark a stream and dependent of itself.