[test] Bump shards on slow bot

R=machenbach@chromium.org

Change-Id: Ib049f88cbbf72fd33b5a962f074ac98948d6ae1c
Reviewed-on: https://chromium-review.googlesource.com/c/1360631Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Tamer Tas <tmrts@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58089}

infra/testing/builders.pyl

@@ -1208,7 +1208,7 @@
       {'name': 'mjsunit_sp_frame_access'},
       {'name': 'mozilla'},
       {'name': 'test262'},
-      {'name': 'v8testing', 'shards': 7},
+      {'name': 'v8testing', 'shards': 8},
       {'name': 'v8testing', 'variant': 'extra', 'shards': 3},
       # Armv8-a.
       {
@@ -1225,7 +1225,7 @@
         'name': 'v8testing',
         'suffix': 'armv8-a',
         'test_args': ['--extra-flags', '--enable-armv8'],
-        'shards': 7
+        'shards': 8
       },
       # Novfp3.
       {
@@ -1245,7 +1245,7 @@
         'suffix': 'novfp3',
         'variant': 'default',
         'test_args': ['--novfp3'],
-        'shards': 7
+        'shards': 8
       },
     ],
   },