[Sheriff] Skip worker test.

BUG=v8:4279
LOG=n
NOTRY=true
TBR=jarin@chromium.org

Review URL: https://codereview.chromium.org/1235493005

Cr-Commit-Position: refs/heads/master@{#29563}

test/mjsunit/mjsunit.status

@@ -250,7 +250,7 @@
   'harmony/rest-params': [PASS, ['no_snap == True', NO_VARIANTS]],
 
   # BUG(v8:4279).
-  'regress/regress-4279': [PASS, ['isolates and mode == debug', FLAKY]],
+  'regress/regress-4279': [PASS, ['isolates', SKIP]],
 }],  # ALWAYS
 
 ['novfp3 == True', {