[d8] Disable worker shutdown test on predictable

The tests rely too much on OS state (thread allocation) to be
predictable.

Change-Id: I9a562369a3c72522630a23ee47e3e819b9411c65
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1725626
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62987}

test/mjsunit/mjsunit.status

@@ -894,6 +894,8 @@
   # Skip tests that are known to be non-deterministic.
   'd8/d8-worker-sharedarraybuffer': [SKIP],
   'd8/d8-os': [SKIP],
+  'd8/d8-worker-shutdown': [SKIP],
+  'd8/d8-worker-shutdown-gc': [SKIP],
   'harmony/futex': [SKIP],
 
   # BUG(v8:7166).