chore: update dependabot to use cron schedule every 6 months

Use the same cron schedule time as the other Github Action
[skip ci]

Author: GerryFerdinandus

.github/dependabot.yml

@@ -1,10 +1,13 @@
-# Enable version updates for GitHub Actions with daily checks
+# Enable version updates for GitHub Actions at cron schedule every 6 months
+# Can be manually triggered via menu: Insights > Dependency graph > "Recent update jobs" -> "Check for updates"
+
 version: 2
 updates:
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
-      interval: "weekly"
+      interval: "cron"
+      cronjob: "0 0 1 1/6 *"
     commit-message:
       prefix: "chore"
       include: "scope"