tools: fix WPT update cron string

The comment says every week, but the actual string defines every day.
Let's set it to one week, as it is quite noisy at the moment.

PR-URL: https://github.com/nodejs/node/pull/57665
Reviewed-By: LiviaMedeiros <livia@cirno.name>
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

.github/workflows/update-wpt.yml

@@ -3,7 +3,7 @@ name: WPT update
 on:
   schedule:
     # Run once a week at 12:00 AM UTC on Sunday.
-    - cron: 0 0 * * *
+    - cron: 0 0 * * 0
   workflow_dispatch:
     inputs:
       subsystems: