[test] Run extra variants on MacOS-arm64

No-Try: true
Bug: chromium:1126457
Change-Id: I3c293afb191a269c5b25d43d68f5f92d93afb410
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2424270
Auto-Submit: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70068}

infra/testing/builders.pyl

@@ -1274,6 +1274,7 @@
     },
     'tests': [
       {'name': 'd8testing'},
+      {'name': 'd8testing', 'variant': 'extra'},
     ],
   },
   'V8 Mac - arm64 - sim - debug': {