Added phpstan workflow

.github/workflows/phpstan.yml

@@ -0,0 +1,23 @@
+name: PHPStan
+
+on: [push]
+
+jobs:
+  analyze:
+    name: Analyze
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v2
+
+    - name: Setup PHP
+      uses: shivammathur/setup-php@v2
+      with:
+        php-version: '8.0'
+
+    - name: Install dependencies
+      run: composer install --prefer-dist --no-progress --no-suggest
+
+    - name: Run PHPStan
+      run: vendor/bin/phpstan