fix cors function for alpine linux

[khassel]

I provide docker images with alpine linux and tested the new cors approach.

It didn't work because after calling

  const dispatcher = new Agent({ connect: { lookup: (_h, _o, cb) => cb(null, address, family) } });

the dispatcher variable was undefined.

This PR solves this and I tested this under debian too.

The mix of internal fetch and newer undici did not work and alpine needs additionally the process.nextTick.

[khassel]

to late to fix this now ...

[KristjanESPERANTO]

Yes, I had that problem with my previous PR and I think I have a solution. Can I add a commit?

[khassel]

sure

[KristjanESPERANTO]

The problem was in the destructuring of undici while requiring it. In the production code const { fetch, Agent } = require("undici") copies the fetch function into a local variable. But in the test code vi.spyOn(undici, "fetch") replaces the property on the module object - so the production code holds its own copy and never sees the spy => tests failed (while production worked). Sounds simple, but it took me a few hours to figure that out for the last PR.

Ah, and on top of that, the spy was originally on global.fetch, which is an entirely different object than undici.fetch after the import change.

[khassel]

This should be merged by @rejas or @sdetweil, as Kristjan and I worked on it, thank you.