tests: webui: Allow file access from files in tests
    
    https://peter.sh/experiments/chromium-command-line-switches/#allow-file-access-from-files
    > By default, file:// URIs cannot read other file:// URIs. This is an
      override for developers who need the old behavior for testing.
    
    Fixes webui tests on CI:
    ```
    Testing test/all_tests.html
    Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check https://xhr.spec.whatwg.org/.
    Access to XMLHttpRequest at 'file:///__w/freeipa/freeipa/install/ui/test/qunit.js' from origin 'null' has been blocked by CORS policy: Cross origin requests are only supported for protocol schemes: http, data, chrome, chrome-untrusted, https.
    Failed to load resource: net::ERR_FAILED
    Access to XMLHttpRequest at 'file:///__w/freeipa/freeipa/install/ui/test/data/i18n_messages.json' from origin 'null' has been blocked by CORS policy: Cross origin requests are only supported for protocol schemes: http, data, chrome, chrome-untrusted, https.
    Failed to load resource: net::ERR_FAILED
    >> Error: Error: Couldn't receive translations
    ```
    
    Related: https://pagure.io/freeipa/issue/9329
    Signed-off-by: Stanislav Levin <slev@altlinux.org>
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>