[DI] Fix PhpDumper generated doc block

src/Symfony/Component/DependencyInjection/Dumper/PhpDumper.php

@@ -628,7 +628,7 @@ EOF;
         }
 
         if ($definition->isAutowired()) {
-            $doc = <<<EOF
+            $doc .= <<<EOF
 
      *
      * This service is autowired.

src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services24.php

@@ -33,6 +33,9 @@ class ProjectServiceContainer extends Container
     /**
      * Gets the 'foo' service.
      *
+     * This service is shared.
+     * This method always returns the same instance of the service.
+     *
      * This service is autowired.
      *
      * @return \Foo A Foo instance