[test] Disable flaky test

Bug: v8:12607
Change-Id: I937366634f77648bb76e36934c5a2952fb0e184f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3450422Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79016}

test/mjsunit/mjsunit.status

@@ -1489,6 +1489,8 @@
   'compiler/deopt-pretenure': [SKIP],
   # BUG(v8:9506): slow tests.
   'wasm/shared-memory-worker-gc-stress': [SKIP],
+  # BUG(v8:12607): flaky test.
+  'harmony/sharedarraybuffer-worker-gc-stress': [SKIP],
 }],  # variant == stress_concurrent_allocation
 
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