ci: keep GitHub Actions up to date with Dependabot

Co-Authored-By: Claude <noreply@anthropic.com>

.github/dependabot.yml

@@ -0,0 +1,13 @@
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: weekly
+    groups:
+      actions:
+        patterns:
+          - '*'
+    commit-message:
+      prefix: ci
+    open-pull-requests-limit: 1