set empty response type to `never`

[gr2m]

If a response has no content key, e.g.

"responses": {
  "204": {
    "description": "Empty response"
  }
}

The resulting type is currently any:

responses: {
  /**
   * Empty response
   */
  "204": any;
};

But I'd argue the better type would be never

[gr2m]

@drwpow I'm working on a pull request for this. I need to update the test/v3/*/github.* files. Is there a trick to do that easily? Maybe you could add instructions to CONTRIBUTING.md? I'm sure I'll figure it out, I only mention it to reduce friction for future contributors

[gr2m]

This one is actually more tricky than I though. The GitHub schema example has lots of responses without a content schema, but I know for a fact that many of these response do have bodies. So instead of setting all responses without a content schema to never, I suggest we set it to never in case of 204 and 3xx response status codes, otherwise to unknown

[alexkrolick]

Revisiting this - are you sure this is an appropriate use of never? That's meant to represent an impossible state, not a valid empty response. What about void or just undefined/null?

https://www.typescriptlang.org/docs/handbook/2/narrowing.html#the-never-type