function getHeaderByName (headers, key) {
  if (Array.isArray(headers)) {
    for (let i = 0; i < headers.length; i += 2) {
      if (headers[i].toLocaleLowerCase() === key.toLocaleLowerCase()) {
        return headers[i + 1]
      }
    }

    return undefined
  } else if (typeof headers.get === 'function') {
    return headers.get(key)
  } else {
    return lowerCaseEntries(headers)[key.toLocaleLowerCase()]
  }
}
@param {import('../../index').Headers|string[]|Record<string, string>} headers
@param {string} key