Add phpstan to the workflow

Author: amaccis

.github/workflows/ci.yml

@@ -17,4 +17,6 @@ jobs:
       - name: Install dependencies
         run: composer install
       - name: Run tests
-        run: vendor/bin/phpunit
+        run: vendor/bin/phpunit
+      - name: Run static analysis
+        run: vendor/bin/phpstan