Fix warning about invalid use of getheader in selenium

  /usr/local/lib/python3.8/dist-packages/selenium/webdriver/remote/remote_connection.py:391: DeprecationWarning: HTTPResponse.getheader() is deprecated and will be removed in urllib3 v2.1.0. Instead use HTTResponse.headers.get(name, default).
    content_type = response.getheader('Content-Type').split(';')