Fix WebTransport close web-platform test to match the spec

Differential Revision: https://phabricator.services.mozilla.com/D168747

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1814750
gecko-commit: 50bedfa293810c1fb23ac8c6b2173a8eddb774db
gecko-reviewers: smaug

webtransport/close.https.any.js

@@ -13,8 +13,8 @@ promise_test(async t => {
 
   const close_info = await wt.closed;
 
-  assert_not_own_property(close_info, 'closeCode');
-  assert_not_own_property(close_info, 'reason');
+  assert_equals(close_info.closeCode, 0 , 'code');
+  assert_equals(close_info.reason, '', 'reason');
 
   await wait(10);
   const data = await query(id);