[test] Un-skip mjsunit/regress/regress-500831.js for GC stress

Issue was fixed in 38088853, re-enabling test.

BUG=v8:5829
NOTRY=true

Review-Url: https://codereview.chromium.org/2643043002
Cr-Commit-Position: refs/heads/master@{#42507}

test/mjsunit/mjsunit.status

@@ -240,9 +240,6 @@
 
   #BUG(v8:5683)
   'wasm/import-memory': [SKIP],
-
-  # Crashes with WASM turned on by default on arm64 gc-stress
-  'regress/regress-500831': [PASS, ['arch == arm64', SKIP]],
 }],  # 'gc_stress == True'
 
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