Predictable Dependabot (#292)

* set dependabot to run at 05:00 UTC on the first Sunday of the month

* switch to known-working syntax

Author: CleanCut

.github/dependabot.yml

@@ -3,9 +3,11 @@ updates:
   - package-ecosystem: "cargo"
     directory: "/"
     schedule:
-      interval: "monthly"
+      interval: "cron"
+      cronjob: "0 5 2 * *" # Second day of each month at 05:00 UTC
 
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
-      interval: "monthly"
+      interval: "cron"
+      cronjob: "0 5 2 * *" # Second day of each month at 05:00 UTC