Dependabot: consolidate GitHub Actions updates to monthly (#909)

* Dependabot: consolidate GitHub Actions updates to monthly

* Fix existing (on main) pre-commit error

Author: rwgk

.github/dependabot.yml

@@ -7,4 +7,15 @@ updates:
   - package-ecosystem: github-actions
     directory: /
     schedule:
-      interval: weekly
+      interval: "monthly"
+      time: "09:00"
+      timezone: "America/Los_Angeles"
+
+    # Keep churn down: only one open PR from this ecosystem at a time
+    open-pull-requests-limit: 1
+
+    groups:
+      actions-monthly:
+        applies-to: version-updates
+        patterns: ["*"]
+        update-types: ["minor", "patch"]