Create build_branch.yml

.github/workflows/build_branch.yml

@@ -0,0 +1,26 @@
+name: Build branch
+run-name: Build branch
+on:
+  push:
+    branches: [ "!main" ]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: install elan
+        run: |
+          set -o pipefail
+          curl -sSfL https://github.com/leanprover/elan/releases/download/v1.4.2/elan-x86_64-unknown-linux-gnu.tar.gz | tar xz
+          ./elan-init -y --default-toolchain none
+          echo "$HOME/.elan/bin" >> $GITHUB_PATH
+      
+      - uses: actions/checkout@v2
+      
+      - name: lake update
+        run: lake update
+        
+      - name: get cache
+        run: lake exe cache get
+      
+      - name: build game
+        run: env LEAN_ABORT_ON_PANIC=1 lake build