Doubling number of shards for 'test262 extra' on 'V8 Linux'

Bug: v8:12538
Change-Id: I57496ee0f50df92000c445c07acc8d6ee763d4e8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3377123Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Liviu Rau <liviurau@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78536}

infra/testing/builders.pyl

@@ -879,7 +879,7 @@
       {'name': 'mozilla', 'variant': 'extra'},
       {'name': 'optimize_for_size'},
       {'name': 'test262', 'shards': 2},
-      {'name': 'test262', 'variant': 'extra'},
+      {'name': 'test262', 'variant': 'extra', 'shards': 2},
       {'name': 'v8initializers'},
       {'name': 'v8testing'},
       {'name': 'v8testing', 'suffix': 'isolates', 'test_args': ['--isolates']},