ci: add lean-action@v1

Author: vEnhance

.github/workflows/lean.yml

@@ -0,0 +1,13 @@
+name: Lean
+
+on:
+  push:
+    branches: ["main"]
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: leanprover/lean-action@v1