Retry network errors/transient HTTP errors in GitHub API requests

[ww-oai]

This adds @octokit/plugin-retry, which we use to retry transient HTTP and network errors when making GitHub API requests.

This should address transient errors like this one:

https://github.com/astral-sh/uv/actions/runs/31519664724/job/93874168058?pr=19979

Excerpted:

 Checking write access for actor 'woodruffw' on astral-sh/uv
  GET /repos/astral-sh/uv/collaborators/woodruffw/permission - 500 with id UNKNOWN in 226ms
  Actor 'woodruffw' is not permitted to run this action: Failed to verify permissions for 'woodruffw': other side closed
  /home/runner/work/_actions/openai/codex-action/52fe01ec70a42f454c9d2ebd47598f9fd6893d56/dist/main.js:27910
            throw new Error(message);
                  ^
  
  Error: Actor 'woodruffw' is not permitted to run this action: Failed to verify permissions for 'woodruffw': other side closed
      at _Command.<anonymous> (/home/runner/work/_actions/openai/codex-action/52fe01ec70a42f454c9d2ebd47598f9fd6893d56/dist/main.js:27910:17)

(Note that the HTTP 500 is a red herring -- Octokit synthesizes a fake HTTP 500 when it encounters an underlying network error.)

The core change here is just two lines, i.e. augmenting the Octokit instance with the plugin and then using it. I've also added tests backstopping the change.

Note: I picked @octokit/plugin-retry because it's an official part of the Octokit SDK that GitHub provides.

[github-actions]

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[ww-oai]

I have read the CLA Document and I hereby sign the CLA