fix name collision in test

Author: staabm

tests/PHPStan/Analyser/nsrt/conditional-vars-php8.php

@@ -2,7 +2,7 @@
 
 declare(strict_types = 1);
 
-namespace ConditionalVars;
+namespace ConditionalVarsPhp8;
 
 use function PHPStan\Testing\assertType;