[test] Increase simdjs test timeout on arm.

TBR=bmeurer@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/1308563010

Cr-Commit-Position: refs/heads/master@{#30504}

test/simdjs/SimdJs.json

@@ -239,7 +239,7 @@
       ]
     }
   ],
-  "timeout_arm": 240,
+  "timeout_arm": 480,
   "timeout_arm64": 120,
   "units": "ms"
 }
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