Error running test-wpt on Windows

[KiChjang]

[vcvarsall.bat] Environment initialized for: 'x64'
 0:03.09 INFO Updating test manifest D:\Workspace\servo\tests\wpt\metadata\MANIFEST.json
 8:58.48 INFO Updating test manifest D:\Workspace\servo\tests\wpt\mozilla\meta\MANIFEST.json
 9:23.93 INFO Updating test manifest D:\Workspace\servo\tests\wpt\webgl\meta\MANIFEST.json
10:30.65 INFO Using 8 client processes
10:33.95 SUITE_START: web-platform-test - running 1 tests
10:33.95 INFO Running reftest tests
10:33.99 INFO Closing logging queue
10:34.00 INFO queue closed
Error running mach:

    ['test-wpt', 'tests\\wpt\\web-platform-tests\\html\\dom\\documents\\dom-tree-accessors\\document.getElementsByName\\document.getElementsByName-liveness.html']

The error occurred in code that was called by the mach command. This is either
a bug in the called code itself or in the way that mach is calling it.

You should consider filing a bug for this issue.

If filing a bug, please include the full output of mach, including this error
message.

The details of the failure are as follows:

TypeError: 'NoneType' object has no attribute '__getitem__'

  File "D:\Workspace\servo\python\servo\testing_commands.py", line 375, in test_wpt
    ret = self.run_test_list_or_dispatch(kwargs["test_list"], "wpt", self._test_wpt, **kwargs)
  File "D:\Workspace\servo\python\servo\testing_commands.py", line 415, in run_test_list_or_dispatch
    return correct_function(**kwargs)
  File "D:\Workspace\servo\python\servo\testing_commands.py", line 401, in _test_wpt
    return self.wptrunner(run_file, **kwargs)
  File "D:\Workspace\servo\python\servo\testing_commands.py", line 447, in wptrunner
    return run_globals["run_tests"](**kwargs)
  File "D:\Workspace\servo\tests\wpt\run.py", line 47, in run_tests
    success = wptrunner.run_tests(**kwargs)
  File "D:\Workspace\servo\tests\wpt\web-platform-tests\tools\wptrunner\wptrunner\wptrunner.py", line 226, in run_tests
    **kwargs)
  File "D:\Workspace\servo\tests\wpt\web-platform-tests\tools\wptrunner\wptrunner\browsers\servo.py", line 36, in browser_kwargs
    "ca_certificate_path": config.ssl_config["ca_cert_path"],

[dralley]

I think this was fixed by #23174 and can be closed