Unit testing: Bad credentials error

I'm using nock to mock HTTP requests following the readme - mocking-the-octokit-client

While my test suite completes successfully, I get the following error message:

::error::Bad credentials
node:internal/process/promises:246
          triggerUncaughtException(err, true /* fromPromise */);
          ^

[UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "HttpError: Bad credentials".] {
  code: 'ERR_UNHANDLED_REJECTION'

Is there something else I need to configure or is it a bug?

// index.js
import * as core from '@actions/core';
import * as github from '@actions/github';

export default async function run() {
    try {
        const myToken = core.getInput('repo_token');
        const octokit = github.getOctokit({ auth: myToken});
        const { data: repos } = await octokit.rest.repos.listPublic();
        return repos;
    }
    catch (error) {
        core.setFailed(error.message);
        throw error;
    }
}

run();

// index.test.js
import nock from 'nock';
import action from './index.js';
import { listPublicRepositories } from './fixtures/list-public-repositories';

describe('action test suite', () => {
  it('It returns a list of public repositories', async () => {

    const repoToken = 'token';
    process.env['INPUT_REPO_TOKEN'] = repoToken;

    nock('https://api.github.com')
      .persist()
      .get('/repositories')
      .reply(200, listPublicRepositories);
    
      const repos = await action();

      expect(repos.length).toBe(1);
      expect(repos[0].id).toBe(1296269);
      expect(repos[0].node_id).toBe("MDEwOlJlcG9zaXRvcnkxMjk2MjY5");
  });
});

Start with index.js and index.test.js, then compare the setup with the linked mocking-the-octokit-client README section. Run the unit test and trace the request and promise handling around action(); done means the mocked test completes without the Bad credentials error or an unhandled promise rejection.