[test] Restrict lite-mode builder to default variant

TBR=sergiyb@chromium.org
NOTRY=true

Bug: v8:8290
Change-Id: Ic82b1f0c8a76f6c046bcc74d0296d7447f773335
Reviewed-on: https://chromium-review.googlesource.com/c/1286675Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56734}

infra/testing/builders.pyl

@@ -206,7 +206,7 @@
   },
   'v8_linux_arm_lite_rel_ng_triggered': {
     'tests': [
-      {'name': 'v8testing', 'shards': 4},
+      {'name': 'v8testing', 'variant': 'default', 'shards': 4},
     ],
   },
   'v8_linux_arm_rel_ng_triggered': {