Provide an overload for unknown responseType

[kschat]

Checklist

• I have read the documentation.
• I have included a pull request description of my changes.
• I have included some tests (more on why this is unchecked below).

Wrapping got is difficult with the current function overloads. The changes made in #1051 made things much better, but given a responseType of 'text' | 'buffer' | 'json' in the following call:

const responseType = 'text' as 'text' | 'buffer' | 'json';
const result = await got({
  url: 'github.com',
  responseType,
});

got will return CancelableRequest<unknown> | Request (or just unknown when awaited) instead of CancelableRequest<Response<unknown>>. This change adds an overload that catches the case where responseType isn't statically known, but we do know that a Response object will be returned.

I haven't added any tests for this PR since this is a type update and I didn't see any tests for types. Given the complexity of the types used by got, though, I'm happy to add some if desired. I've had good luck using conditional-type-checks for testing types in the past.

Related issues:
#954
#1122

[szmarczak]

@kschat Can you also submit a test for this particular use case?

[kschat]

@szmarczak sorry for the delayed response. I'm happy to open another PR with a test if that's still needed.

[szmarczak]

Sure, that would be great.