Mark TestCase::$backupGlobals as nullable

Author: morozov

src/Framework/TestCase.php

@@ -60,7 +60,7 @@ abstract class TestCase extends Assert implements SelfDescribing, Test
     private const LOCALE_CATEGORIES = [\LC_ALL, \LC_COLLATE, \LC_CTYPE, \LC_MONETARY, \LC_NUMERIC, \LC_TIME];
 
     /**
-     * @var bool
+     * @var null|bool
      */
     protected $backupGlobals;