Added phpstan

Signed-off-by: buchwasa <17461354+buchwasa@users.noreply.github.com>

.github/workflows/phpstan.yml

@@ -0,0 +1,26 @@
+name: PHPStan
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Validate composer.json and composer.lock
+      run: composer validate
+    - name: Cache Composer packages
+      id: composer-cache
+      uses: actions/cache@v2
+      with:
+        path: vendor
+        key: ${{ runner.os }}-php-${{ hashFiles('**/composer.lock') }}
+        restore-keys: |
+          ${{ runner.os }}-php-
+    - name: Install dependencies
+      if: steps.composer-cache.outputs.cache-hit != 'true'
+      run: composer install --prefer-dist --no-progress --no-suggest
+    - name: Run phpstan
+      run: composer run-script phpstan