Paginate does not pass through custom accept headers

Bug Report

Current Behavior

When setting a custom Accept header, the paginate function does not use the value in any request but the first.

octokit.paginate(
  octokit.apps.getInstallationRepositories({
    per_page: 100,
    headers: {
      accept: 'application/vnd.github.machine-man-preview+json,application/vnd.github.mercy-preview+json'
    }
  }),
  (res) => res.data.repositories
)

Expected behavior/code

Every request that paginate makes uses the custom headers defined.

Environment

• Probot version(s): 7.2.0
• Node/npm version: Node 10.13.0
• OS: macOS

Related Octokit / Probot links

• https://github.com/probot/probot/blob/master/src/github/pagination.ts#L24
• https://github.com/octokit/rest.js/blob/v15.15.1/lib/plugins/pagination/get-next-page.js
• https://github.com/octokit/rest.js/blob/v15.15.1/lib/plugins/pagination/get-page.js

[gr2m]

Yes we do that via #744 but we keep the old one around and log a deprecation warning to make it easier for folks to upgrade

[gr2m]

That should work as expected with Probot 9, note that the API changed. The old API is still working, but logs a deprecation message