Add final test

Author: VincentLanglet

tests/PHPStan/Analyser/nsrt/is-subclass-of.php

@@ -53,3 +53,11 @@ function (string $a, string $b, string $c, string $d) {
 class Foo {}
 
 class Bar extends Foo {}
+
+final class FinalFoo {}
+
+function (FinalFoo $a) {
+	if (is_subclass_of($a, FinalFoo::class)) {
+		\PHPStan\Testing\assertType('*NEVER*', $a);
+	}
+};