Doesn't play nice with node v18 undici fetch #533

In Node 18 the standards-compliant undici fetch is available, and it accepts Node's Readable Stream as a body as well as the standard Web Streams.

The problem is that new FormData() doesn't return an object that is recognized as a Readable.

Workaround:

import {PassThrough} from 'stream'
// ...
const pt = new PassThrough()
formData.pipe(pt)
fetch(url, {
  // ...
  body: pt
})

You can test the problem in Node 18 by running the following, which will throw:

import {Readable} from 'stream'
// ...
Readable.toWeb(formData)

Probably Readable needs to be in the prototype chain?