gactions: run PHPStan check

.github/workflows/build.yml

@@ -0,0 +1,37 @@
+name: "Build"
+
+on:
+  pull_request:
+  push:
+
+jobs:
+  phpstan:
+    name: PHPStan
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Setup PHP with pecl extension
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '7.4'
+
+      - name: Get composer cache directory
+        id: composercache
+        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+      - name: Cache dependencies
+        uses: actions/cache@v2
+        with:
+          path: ${{ steps.composercache.outputs.dir }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
+          restore-keys: ${{ runner.os }}-composer-
+
+      - name: Install dependencies
+        run: composer install --prefer-dist
+
+      - name: Run PHPStan
+        run: composer phpstan