fix unset on stdClass

Author: staabm

src/Rules/Variables/UnsetRule.php

@@ -89,7 +89,7 @@ private function canBeUnset(Node $node, Scope $scope): ?IdentifierRuleError
 						->build();
 				}
 
-				if (!$classReflection->hasProperty($node->name->name)) {
+				if (!$classReflection->hasNativeProperty($node->name->name)) {
 					continue;
 				}
 

tests/PHPStan/Rules/Variables/data/bug-12421.php

@@ -93,5 +93,9 @@ function doFoo() {
 	$x = new PhpdocImmutableClass();
 	unset($x->y);
 	var_dump($x->y);
+
+	$x = new \stdClass();
+	unset($x->y);
+
 }