[test] Bump shards on slow bot

TBR=sergiyb@chromium.org
NOTRY=true

Change-Id: I74a1f7a66ee31ea4e6b02286de2f99c75f596027
Reviewed-on: https://chromium-review.googlesource.com/c/1354879Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57926}

infra/testing/builders.pyl

@@ -339,8 +339,8 @@
   'v8_linux_arm64_dbg': {
     'tests': [
       {'name': 'mjsunit_sp_frame_access'},
-      {'name': 'mozilla'},
-      {'name': 'test262'},
+      {'name': 'mozilla', 'shards': 2},
+      {'name': 'test262', 'shards': 2},
       {'name': 'v8testing', 'shards': 10},
       {'name': 'v8testing', 'variant': 'extra', 'shards': 6},
     ],
@@ -1264,8 +1264,8 @@
   'V8 Linux - arm64 - sim - debug': {
     'tests': [
       {'name': 'mjsunit_sp_frame_access'},
-      {'name': 'mozilla'},
-      {'name': 'test262'},
+      {'name': 'mozilla', 'shards': 2},
+      {'name': 'test262', 'shards': 2},
       {'name': 'v8testing', 'shards': 10},
       {'name': 'v8testing', 'variant': 'extra', 'shards': 6},
     ],