[infra] add mozilla shards for {V8 Linux - arm - sim - debug}

Mozilla suite acts as the bottleneck for this bot.

This CL bumps the shards for the Mozilla suite.

TBR=machenbach@chromium.org

Bug: v8:9633
Change-Id: Ia73b2688b29a3387cc69fa8f79c008f6bf0114cd
No-Try: True
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1760824Reviewed-by: Tamer Tas <tmrts@chromium.org>
Commit-Queue: Tamer Tas <tmrts@chromium.org>
Auto-Submit: Tamer Tas <tmrts@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63262}

infra/testing/builders.pyl

@@ -1391,7 +1391,7 @@
     },
     'tests': [
       {'name': 'mjsunit_sp_frame_access', 'shards': 4},
-      {'name': 'mozilla'},
+      {'name': 'mozilla', 'shards': 4},
       {'name': 'test262'},
       {'name': 'v8testing', 'shards': 8},
       {'name': 'v8testing', 'variant': 'extra', 'shards': 4},