Fix PDOStatement::fetchObject() stub

Closes GH-6449.

Author: BenMorel

ext/pdo/pdo_stmt.stub.php

@@ -40,7 +40,7 @@ public function fetchAll(int $mode = PDO::FETCH_BOTH, mixed ...$args) {}
     /** @return mixed */
     public function fetchColumn(int $column = 0) {}
 
-    /** @return mixed */
+    /** @return object|false */
     public function fetchObject(?string $class = "stdClass", ?array $ctorArgs = null) {}
 
     /** @return mixed */

ext/pdo/pdo_stmt_arginfo.h

@@ -1,5 +1,5 @@
 /* This is a generated file, edit the .stub.php file instead.
- * Stub hash: 574055f1dbb6a1bee10e4476642a759e53ca2802 */
+ * Stub hash: 9d890849a08b43cb35e2cd8468aeaabfc0a7f218 */
 
 ZEND_BEGIN_ARG_INFO_EX(arginfo_class_PDOStatement_bindColumn, 0, 0, 2)
 	ZEND_ARG_TYPE_MASK(0, column, MAY_BE_STRING|MAY_BE_LONG, NULL)