Add phpstan action step

Author: mkoziy

.github/workflows/tests.yml renamed to .github/workflows/ci.yml

@@ -1,12 +1,12 @@
-name: tests
+name: CI
 
 on:
   push:
     branches: [ main ]
   pull_request:
 
 jobs:
-  phpunit:
+  ci:
     runs-on: ubuntu-latest
     strategy:
       matrix:
@@ -26,4 +26,8 @@ jobs:
         run: composer install --no-progress --no-suggest --prefer-dist
 
       - name: Run PHPUnit
-        run: vendor/bin/phpunit tests
+        run: vendor/bin/phpunit tests
+
+      - name: Run PHPStan
+        run: vendor/bin/phpstan analyse src
+