Change dependabot schedule

Author: crtschin

.github/dependabot.yml

@@ -3,8 +3,8 @@ updates:
   - package-ecosystem: "nix"
     directory: "/"
     schedule:
-      interval: "weekly"
-      day: "monday"
+      interval: "cron"
+      cronjob: "0 9 * * SAT#1"
     commit-message:
       prefix: "nix"
     cooldown:
@@ -17,8 +17,8 @@ updates:
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
-      interval: "weekly"
-      day: "monday"
+      interval: "cron"
+      cronjob: "0 9 * * SAT#1"
     commit-message:
       prefix: "ci"
     cooldown: