workflows/scorecard: Run this job once per day instead of for every push

We started going over our API limits and suspect this was the cause.
For now, we'll run it once a day while we sort this out.

Author: tstellar

.github/workflows/scorecard.yml

@@ -12,9 +12,7 @@ on:
   # To guarantee Maintained check is occasionally updated. See
   # https://github.com/ossf/scorecard/blob/main/docs/checks.md#maintained
   schedule:
-    - cron: '38 20 * * 4'
-  push:
-    branches: [ "main" ]
+    - cron: '38 20 * * *'
 
 # Declare default permissions as read only.
 permissions: