[wasm] Skip slow test on TSan

TBR=titzer@chromium.org

No-Try: true
Bug: v8:9506
Change-Id: Id8ab56654395ad6e8fd6f9bef8830f0efffda2f0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1706479Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62775}

test/mjsunit/mjsunit.status

@@ -584,6 +584,9 @@
   'es6/block-conflicts-sloppy': [PASS, SLOW],
   'math-floor-part1': [PASS, SLOW],
   'regress/regress-500980': [PASS, SLOW],
+
+  # BUG(v8:9506): times out.
+  'wasm/shared-memory-worker-explicit-gc-stress': [SKIP],
 }],  # 'tsan == True'
 
 ##############################################################################