ci: monitor dependencies

.github/dependabot.yml

+version: 2
+updates:
+  # Maintain dependencies for GitHub Actions
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"
+    ignore:
+      # Offical actions have moving tags like v1
+      # that are used, so they don't need updates here
+      - dependency-name: "actions/*"