minor #21663 Updated PHPUnit namespaces (peterrehm)

This PR was squashed before being merged into the 2.8 branch (closes #21663).

Discussion
----------

Updated PHPUnit namespaces

| Q             | A
| ------------- | ---
| Branch?       | 2.8
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Follow Up of #21564

Commits
-------

205ced4 Updated PHPUnit namespaces

Author: nicolas-grekas

Tests/Compiler/AutowirePassTest.php

@@ -11,14 +11,15 @@
 
 namespace Symfony\Component\DependencyInjection\Tests\Compiler;
 
+use PHPUnit\Framework\TestCase;
 use Symfony\Component\DependencyInjection\Compiler\AutowirePass;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Reference;
 
 /**
  * @author Kévin Dunglas <[email protected]>
  */
-class AutowirePassTest extends \PHPUnit_Framework_TestCase
+class AutowirePassTest extends TestCase
 {
     public function testProcess()
     {

Tests/Loader/DirectoryLoaderTest.php

@@ -11,6 +11,7 @@
 
 namespace Symfony\Component\DependencyInjection\Tests\Loader;
 
+use PHPUnit\Framework\TestCase;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Loader\PhpFileLoader;
 use Symfony\Component\DependencyInjection\Loader\IniFileLoader;
@@ -19,7 +20,7 @@
 use Symfony\Component\Config\Loader\LoaderResolver;
 use Symfony\Component\Config\FileLocator;
 
-class DirectoryLoaderTest extends \PHPUnit_Framework_TestCase
+class DirectoryLoaderTest extends TestCase
 {
     private static $fixturesPath;