Tests bootstrap - require InstalledVersions only if it's not declared yet (#11014)

tests/bootstrap.php

@@ -10,6 +10,7 @@
  * file that was distributed with this source code.
  */
 
+use Composer\InstalledVersions;
 use Composer\Util\Platform;
 
 error_reporting(E_ALL);
@@ -19,7 +20,11 @@ if (function_exists('date_default_timezone_set') && function_exists('date_defaul
 }
 
 require __DIR__.'/../src/bootstrap.php';
-require __DIR__.'/../src/Composer/InstalledVersions.php';
+
+if (!class_exists(InstalledVersions::class, false)) {
+    require __DIR__.'/../src/Composer/InstalledVersions.php';
+}
+
 require __DIR__.'/Composer/Test/TestCase.php';
 
 Platform::putEnv('COMPOSER_TESTS_ARE_RUNNING', '1');