ci: add Dependabot config for github-actions updates

.github/dependabot.yml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"

.github/workflows/dependabot-auto-merge.yml

@@ -0,0 +1,24 @@
+name: Dependabot auto-merge
+
+on:
+  pull_request_target:
+    branches:
+      - master
+      - main
+    types:
+      - opened
+
+permissions:
+  pull-requests: write
+  contents: write
+
+jobs:
+  enableAutoMerge:
+    runs-on: ubuntu-latest
+    if: github.event.pull_request.user.login == 'dependabot[bot]'
+    steps:
+      - name: Enable auto-merge for Dependabot PRs
+        run: gh pr merge --auto --merge "$PR_URL"
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}