[test] Bump shards for slow tests

Prevent timeouts like:
https://ci.chromium.org/p/v8/builders/luci.v8.ci/V8%20Linux%20-%20debug/23124

TBR=sergiyb@chromium.org
NOTRY=true

Change-Id: I550a0d85366aa7171e2e23b2f6d2482ec953eb52
Reviewed-on: https://chromium-review.googlesource.com/c/1333672Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57471}

infra/testing/builders.pyl

@@ -127,7 +127,7 @@
       {'name': 'mozilla', 'variant': 'extra'},
       {'name': 'optimize_for_size'},
       {'name': 'test262_variants', 'shards': 4},
-      {'name': 'test262_variants', 'variant': 'extra', 'shards': 2},
+      {'name': 'test262_variants', 'variant': 'extra', 'shards': 3},
       {'name': 'v8testing', 'shards': 2},
       {'name': 'v8testing', 'suffix': 'isolates', 'test_args': ['--isolates'], 'shards': 2},
       {'name': 'v8testing', 'variant': 'extra'},
@@ -285,7 +285,7 @@
       {'name': 'mjsunit_sp_frame_access'},
       {'name': 'optimize_for_size'},
       {'name': 'test262_variants', 'shards': 4},
-      {'name': 'test262_variants', 'variant': 'extra', 'shards': 2},
+      {'name': 'test262_variants', 'variant': 'extra', 'shards': 3},
       {'name': 'v8initializers'},
       {'name': 'v8testing', 'shards': 2},
       {'name': 'v8testing', 'variant': 'extra'},
@@ -574,7 +574,7 @@
       {'name': 'optimize_for_size'},
       {'name': 'test262_variants', 'shards': 6},
       {'name': 'test262_variants', 'variant': 'code_serializer', 'shards': 2},
-      {'name': 'test262_variants', 'variant': 'extra', 'shards': 2},
+      {'name': 'test262_variants', 'variant': 'extra', 'shards': 3},
       {'name': 'v8testing', 'shards': 3},
       {
         'name': 'v8testing',
@@ -778,7 +778,7 @@
       {'name': 'mozilla', 'variant': 'extra'},
       {'name': 'optimize_for_size'},
       {'name': 'test262_variants', 'shards': 5},
-      {'name': 'test262_variants', 'variant': 'extra', 'shards': 2},
+      {'name': 'test262_variants', 'variant': 'extra', 'shards': 3},
       {'name': 'v8testing', 'shards': 2},
       {'name': 'v8testing', 'variant': 'extra'},
       {'name': 'v8testing', 'variant': 'minor_mc', 'shards': 1},