`github.request()` should respect custom headers like `Accept`, `Authorization` etc.

[tlenex]

Is your feature request related to a problem? Please describe. I'd like to make custom, external request with custom headers for fetching data using github.request() in my github-script. However, the method is ignoring custom HTTP headers provided in it's options like Accept and Authorization - I didn't check any others User-agent might also be the case.

Describe the solution you'd like Script like this:

github.request('POST https://example.com', {
  // I want headers to be like this:
  headers: {
    authorization: 'Bearer xxx',
    accept: 'application/vnd.heroku+json; version=3',
    'content-type': 'application/json'
  }
});

Could respect given headers in the request options. It would be a really nice way of fetching data in github-script without usage of additional steps/libs/dependencies.

Describe alternatives you've considered Using bash step with curl or exec.exec('curl'); in github-script step, but both feel clunky in this case. Installing node deps like node-fetch seems like a waste of time and resources, especially when github.request() is using exactly node-fetch under the hood, but we just can't access it.

Additional context https://stackoverflow.com/questions/72815672/cant-override-some-http-headers-with-github-request-in-actions-github-script