test: skip flaky parts of broadcastchannel test on Windows

The feature was added recently and is experimental. This will need to be
fixed before it can be released as stable (in my opinion at least). But
for now, this gets us to a green CI without skipping the parts of the
test that are working on Windows.

PR-URL: https://github.com/nodejs/node/pull/36386


Reviewed-By: Beth Griggs <bgriggs@redhat.com>
Reviewed-By: Richard Lau <rlau@redhat.com>