Support the latest Octokit in `@actions/github`

[joshmgross]

The latest Octokit only supports Node 18 and higher - https://github.com/orgs/octokit/discussions/44

Actions currently supports Node 16 and 20 - https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/

We should update @actions/github to the latest version of Octokit and drop support for Node 16 so that actions can transition to Node 20. This will be a breaking change.

[joshmgross]

This should be available with v6 from #1553

https://github.com/actions/toolkit/blob/main/packages/github/RELEASES.md#600

Thanks @takost!