[test] Bump shards on slow bot

TBR=tmrts@chromium.org,liviurau@chromium.org
NOTRY=true

Change-Id: I2ab31012de34716d50586ef44da43a0bc8f89ac6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1826719Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63982}

infra/testing/builders.pyl

@@ -43,7 +43,7 @@
       {'name': 'v8testing', 'variant': 'default', 'shards': 4},
       {'name': 'v8testing', 'variant': 'trusted', 'shards': 4},
       {'name': 'mozilla', 'variant': 'default'},
-      {'name': 'test262_variants', 'variant': 'default', 'shards': 7},
+      {'name': 'test262_variants', 'variant': 'default', 'shards': 9},
     ],
   },
   ##############################################################################
@@ -1240,7 +1240,7 @@
     },
     'tests': [
       {'name': 'mozilla', 'variant': 'default'},
-      {'name': 'test262', 'variant': 'default', 'shards': 6},
+      {'name': 'test262_variants', 'variant': 'default', 'shards': 8},
       {'name': 'v8testing', 'variant': 'default', 'shards': 3},
       {'name': 'v8testing', 'variant': 'trusted', 'shards': 3},
     ],