[infra] Double the shards for v8_linux64_heap_sandbox_dbg_ng_triggered

Bug: v8:12692
Change-Id: I41cc3b8f059d1c6dc28c6ddd14998c959b4d36ae
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3652296
Auto-Submit: Almothana Athamneh <almuthanna@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80595}

infra/testing/builders.pyl

@@ -441,7 +441,7 @@
       'os': 'Ubuntu-18.04',
     },
     'tests': [
-      {'name': 'v8testing', 'shards': 2},
+      {'name': 'v8testing', 'shards': 4},
     ],
   },
   'v8_linux64_msan_rel_ng_triggered': {