TestStream is a Node stream but docs link to web ReadableStream

### Affected URL(s)

https://nodejs.org/api/test.html#class-testsstream

### Description of the problem

The docs for `TestsStream` say `<extends ReadableStream>` which links to the Web Streams API `ReadableStream` page.

However, `TestsStream` is **not** a Web Stream `ReadableStream`, it is actually a Node Stream `Readable`.