Skip wpt failing tests

Some of Mac10.12 Tests have started failing consistently starting from
build: [1]. Primary suspect is crrev.com/c/3163618. But as per this CL's
description and as the CL is large, skipping was preferred.

[1] https://ci.chromium.org/ui/p/chromium/builders/ci/Mac10.12%20Tests/46388/overview

Bug: 1250215
Change-Id: I6b62d28936b8caee6459215c2a6cafb65eb677cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3163259
Owners-Override: Omar Morsi <omorsi@google.com>
Auto-Submit: Omar Morsi <omorsi@google.com>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#922082}

third_party/blink/web_tests/W3CImportExpectations

@@ -452,4 +452,7 @@ virtual/not-plz-service-worker/external/wpt/service-workers/idlharness.https.any
 virtual/not-plz-service-worker/external/wpt/service-workers/idlharness.https.any.worker.html [ Skip ]
 virtual/plz-dedicated-worker/external/wpt/service-workers/idlharness.https.any.sharedworker.html [ Skip ]
 virtual/plz-dedicated-worker/external/wpt/service-workers/idlharness.https.any.worker.html [ Skip ]
-virtual/portals/external/wpt/portals/idlharness.window.html [ Skip ]
+virtual/portals/external/wpt/portals/idlharness.window.html [ Skip ]
+external/wpt/webtransport/idlharness.any.html [ Skip ]
+external/wpt/webtransport/idlharness.any.sharedworker.html [ Skip ]
+external/wpt/webtransport/idlharness.any.worker.html [ Skip ]