ci: add electron build to CI

.github/workflows/build.yml

@@ -50,3 +50,29 @@ jobs:
         if: steps.cache.outputs.cache-hit != 'true'
       - name: Build Web
         run: ./bin/package-browser
+
+  electron:
+    strategy:
+      matrix:
+        os:
+          - ubuntu-latest
+          - windows-latest
+          - macos-latest
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v2
+      - name: Install node
+        uses: actions/setup-node@v1
+        with:
+          node-version: 16
+      - name: Cache
+        uses: actions/cache@v2
+        id: cache
+        with:
+          path: '**/node_modules'
+          key: yarn-v1-${{ hashFiles('**/yarn.lock') }}
+      - name: Install
+        run: yarn --immutable
+        if: steps.cache.outputs.cache-hit != 'true'
+      - name: Build Electron
+        run: ./bin/package