Increase timeout for JSTests on arm64

R=ulan@chromium.org

Bug: chromium:936713
Change-Id: If3361023fa6fecfc070028ef505ca1ab1ec1d568
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1505800Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Sergiy Belozorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60066}

test/js-perf-test/JSTests.json

@@ -5,6 +5,7 @@
   "run_count_arm": 1,
   "run_count_arm64": 1,
   "timeout": 120,
+  "timeout_arm64": 240,
   "units": "score",
   "total": true,
   "resources": ["base.js"],