Fix dependabot workflow

Author: purejava

.github/workflows/dependabot.yml

@@ -5,3 +5,15 @@ updates:
     schedule:
       interval: "weekly"
       day: "saturday"
+      time: "08:00"
+      timezone: "Etc/UTC"
+
+  - package-ecosystem: "github-actions"
+    directory: "/" # even for `.github/workflows`
+    schedule:
+      interval: "monthly"
+    groups:
+      github-actions:
+        patterns:
+          - "*"
+