[test] Bump shards on slow builders

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

Change-Id: I7f345ce40b7906a71f960c3e8f3ab11974d9ac80
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1932370Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65146}

infra/testing/builders.pyl

@@ -249,7 +249,7 @@
     'tests': [
       {'name': 'test262', 'shards': 7},
       {'name': 'v8testing', 'shards': 3},
-      {'name': 'v8testing', 'variant': 'extra', 'shards': 2},
+      {'name': 'v8testing', 'variant': 'extra', 'shards': 3},
       {'name': 'v8testing', 'variant': 'slow_path'},
     ],
   },
@@ -1011,7 +1011,7 @@
     'tests': [
       {'name': 'test262', 'shards': 5},
       {'name': 'v8testing', 'shards': 2},
-      {'name': 'v8testing', 'variant': 'extra'},
+      {'name': 'v8testing', 'variant': 'extra', 'shards': 2},
       {'name': 'v8testing', 'variant': 'slow_path', 'shards': 1},
     ],
   },