[test] Bump shards on slow trybot

NOTRY=true
TBR=sergiyb@chromium.org

Change-Id: I7f87b58242fa2e29166c11aacc235ef9c279b3e8
Reviewed-on: https://chromium-review.googlesource.com/c/1301478Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57030}

infra/testing/builders.pyl

@@ -336,8 +336,8 @@
       {'name': 'mjsunit_sp_frame_access'},
       {'name': 'mozilla'},
       {'name': 'test262'},
-      {'name': 'v8testing', 'shards': 7},
-      {'name': 'v8testing', 'variant': 'extra', 'shards': 3},
+      {'name': 'v8testing', 'shards': 10},
+      {'name': 'v8testing', 'variant': 'extra', 'shards': 6},
     ],
   },
   'v8_linux_arm64_gc_stress_dbg': {