Dependabot config and cron update, pre-commit-update cron update (#62)

Author: kattni

.github/dependabot.yml

@@ -4,7 +4,6 @@ updates:
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
-      # Check for updates on Sunday, 8PM UTC
-      interval: "weekly"
-      day: "sunday"
-      time: "20:00"
+      # Check for updates on the first Sunday of every month, 8PM UTC
+      interval: "cron"
+      cronjob: "0 20 * * sun#1"

.github/workflows/pre-commit-update.yml

@@ -2,7 +2,10 @@ name: Update pre-commit
 
 on:
   schedule:
-    - cron: "0 20 * * SUN"  # Sunday @ 2000 UTC
+    - cron: "0 20 1-7 * */7"  # First Sunday of the month @ 2000 UTC
+      # Reading this expression: At 20:00 on every day-of-month from 1 through 7 if
+      # it's on every 7th day-of-week, i.e. any one of the first seven days of the
+      # month as long as it is a Sunday.
   workflow_dispatch:
 
 jobs: