Update bug-13747.php

Author: staabm

tests/PHPStan/Analyser/nsrt/bug-13747.php

@@ -1,6 +1,7 @@
 <?php declare(strict_types = 1);
 
-use function PHPStan\dumpType;
+namespace Bug13747;
+
 use function PHPStan\Testing\assertType;
 
 class HelloWorld