Add phpunit configuration file

Use the configuration file to pass the location of the tests and
autoload class files.

Pass -sp to phpcs command

.github/workflows/php.yml

@@ -15,8 +15,8 @@ jobs:
       - name: Install dependencies
         run: composer install --prefer-dist --no-interaction --ansi
 
-      - name: Run tests
-        run: php${{ matrix.php }} ./vendor/bin/phpunit tests/php/*
-
       - name: Running phpcs
         run: composer run-script cs
+
+      - name: Run tests
+        run: php${{ matrix.php }} ./vendor/bin/phpunit