chore: Run update-contributors workflow once a month (#4679)

Current schedule is too often: the first week of every month and
every Sunday. This modification is just for the 1st of the month
at 00:00.

Author: jake-kramer

.github/workflows/update-contributors.yml

@@ -2,7 +2,7 @@ name: Update Contributors in README
 
 on:
   schedule:
-    - cron: '0 0 1-7 * SUN'
+    - cron: '0 0 1 * *'
   workflow_dispatch:
 
 permissions: