PHP 8.3 | InstalledVersionsTest: fix deprecation notice

Calling `ReflectionProperty::setValue()` with only one argument (to set a static property) is deprecated.
Passing `null` as the first (`$object`) parameter will work cross-version.

Ref: https://wiki.php.net/rfc/deprecate_functions_with_overloaded_signatures#reflectionpropertysetvalue

tests/Composer/Test/InstalledVersionsTest.php

@@ -33,14 +33,14 @@ public static function setUpBeforeClass(): void
         $prop = new \ReflectionProperty('Composer\Autoload\ClassLoader', 'registeredLoaders');
         $prop->setAccessible(true);
         self::$previousRegisteredLoaders = $prop->getValue();
-        $prop->setValue([]);
+        $prop->setValue(null, []);
     }
 
     public static function tearDownAfterClass(): void
     {
         $prop = new \ReflectionProperty('Composer\Autoload\ClassLoader', 'registeredLoaders');
         $prop->setAccessible(true);
-        $prop->setValue(self::$previousRegisteredLoaders);
+        $prop->setValue(null, self::$previousRegisteredLoaders);
         InstalledVersions::reload(null); // @phpstan-ignore-line
     }