Update Dependabot schedule

This commit updates the timing of when Dependabot does its weekly
checks.

Ref:
- https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#configuration-options-for-the-dependabotyml-file

.github/dependabot.yml

@@ -1,10 +1,16 @@
+---
 version: 2
+
 updates:
   - package-ecosystem: "bundler"
     directory: "/"
     schedule:
-      interval: "weekly"
+      interval: weekly
+      time: "02:00"
+      timezone: "Etc/UTC"
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
-      interval: "weekly"
+      interval: weekly
+      time: "02:00"
+      timezone: "Etc/UTC"