minor #22663 [DI] Fix PhpDumper blank lines around namespace (ogizanagi)

This PR was merged into the 2.7 branch.

Discussion
----------

[DI] Fix PhpDumper blank lines around namespace

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A

219bce9 tries to fix CS in an expected PhpDumper output, which actually shows the PhpDumper does not create proper blank lines around the namespace.
That's why tests are failing on #22660.

Commits
-------

c9f6c16 [DI] Fix PhpDumper blank lines around namespace

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

@@ -827,7 +827,7 @@ private function addNewInstance($id, Definition $definition, $return, $instantia
     private function startClass($class, $baseClass, $namespace)
     {
         $bagClass = $this->container->isFrozen() ? 'use Symfony\Component\DependencyInjection\ParameterBag\FrozenParameterBag;' : 'use Symfony\Component\DependencyInjection\ParameterBag\\ParameterBag;';
-        $namespaceLine = $namespace ? "namespace $namespace;\n" : '';
+        $namespaceLine = $namespace ? "\nnamespace $namespace;\n" : '';
 
         return <<<EOF
 <?php