[DependencyInjection] fix the ValidateEnvPlaceHolderPassTest that was using a deprecated path for TreeBuilder

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

@@ -332,7 +332,7 @@ class EnvConfigurationWithoutRootNode implements ConfigurationInterface
 {
     public function getConfigTreeBuilder()
     {
-        return new TreeBuilder();
+        return new TreeBuilder('env_extension');
     }
 }
 
@@ -340,8 +340,8 @@ class ConfigurationWithArrayNodeRequiringOneElement implements ConfigurationInte
 {
     public function getConfigTreeBuilder()
     {
-        $treeBuilder = new TreeBuilder();
+        $treeBuilder = new TreeBuilder('env_extension');
-        $treeBuilder->root('env_extension')
+        $treeBuilder->getRootNode()
             ->children()
                 ->arrayNode('nodes')
                     ->isRequired()