Fix: Use PHPUnit\TestFixture as namespace for test fixtures

Author: localheinz

tests/end-to-end/cli/_files/MyCommand.php

@@ -7,6 +7,8 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+namespace PHPUnit\TestFixture;
+
 use PHPUnit\TextUI\Command;
 
 class MyCommand extends Command

tests/end-to-end/cli/mycommand.phpt

@@ -10,9 +10,9 @@ $_SERVER['argv'][] = \realpath(__DIR__ . '/../../_files/BankAccountTest.php');
 
 require_once __DIR__ . '/../../bootstrap.php';
 
-MyCommand::main();
+PHPUnit\TestFixture\MyCommand::main();
 --EXPECTF--
-MyCommand::myHandler 123
+PHPUnit\TestFixture\MyCommand::myHandler 123
 PHPUnit %s #StandWithUkraine
 
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