async function readOrFetch(localUrl, remoteUrl) {
  try {
    return String(await fs.readFile(localUrl))
  } catch (error) {
    const exception = /** @type {NodeJS.ErrnoException} */ (error)
    if (exception.code !== 'ENOENT') {
      throw exception
    }
  }

  try {
    const response = await fetch(remoteUrl, {
      headers: {Authorization: 'bearer ' + ghKey}
    })
    const responseText = await response.text()
    await fs.writeFile(localUrl, responseText)
    return responseText
  } catch (error) {
    console.error('Could not fetch `%s`', remoteUrl, error)
  }
}
Get a file.

@param {Readonly<URL>} localUrl
  URL to file system.
@param {Readonly<URL>} remoteUrl
  URL to remote.
@returns {Promise<string | undefined>}
  Content, if local or remote.