minor symfony#31944 [DI] Fix suspicious test (ro0NL)

This PR was merged into the 4.2 branch.

Discussion
----------

[DI] Fix suspicious test

| Q             | A
| ------------- | ---
| Branch?       | 4.2
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | symfony#31942
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->

cc @nicolas-grekas

Commits
-------

25b961a [DI] Fix suspicious test

Author: nicolas-grekas

src/Symfony/Component/Config/Definition/Exception/TreeWithoutRootNodeException.php

@@ -13,6 +13,8 @@
 
 /**
  * @author Roland Franssen <franssen.roland@gmail.com>
+ *
+ * @internal
  */
 class TreeWithoutRootNodeException extends \RuntimeException
 {

src/Symfony/Component/DependencyInjection/Tests/Compiler/ValidateEnvPlaceholdersPassTest.php

@@ -226,16 +226,15 @@ public function testEnvWithVariableNode(): void
 
     /**
      * @group legacy
+     * @expectedDeprecation A tree builder without a root node is deprecated since Symfony 4.2 and will not be supported anymore in 5.0.
      */
     public function testConfigurationWithoutRootNode(): void
     {
         $container = new ContainerBuilder();
         $container->registerExtension(new EnvExtension(new EnvConfigurationWithoutRootNode()));
-        $container->loadFromExtension('env_extension');
+        $container->loadFromExtension('env_extension', ['foo' => 'bar']);
 
-        $this->doProcess($container);
-
-        $this->addToAssertionCount(1);
+        (new ValidateEnvPlaceholdersPass())->process($container);
     }
 
     public function testEmptyConfigFromMoreThanOneSource()
@@ -332,7 +331,7 @@ class EnvConfigurationWithoutRootNode implements ConfigurationInterface
 {
     public function getConfigTreeBuilder()
     {
-        return new TreeBuilder('env_extension');
+        return new TreeBuilder();
     }
 }