Add auto update

.github/workflows/update.yml

@@ -0,0 +1,22 @@
+name: Update
+
+on:
+  schedule:
+    - cron: "0 8 * * 0" # at 08:00 (UTC) on Sunday
+  workflow_dispatch:
+
+jobs:
+  update:
+    runs-on: ubuntu-latest
+
+    permissions:
+      contents: write
+      issues: write
+      pull-requests: write
+
+    steps:
+      - uses: actions/checkout@v4
+      - uses: oliver-butterley/lean-update@v1-alpha
+        with:
+          on_update_succeeds: pr
+          on_update_fails: issue