Fix `\yii\db\QueryTrait` type hints (#13956) [skip ci]

framework/db/QueryTrait.php

@@ -376,7 +376,7 @@ trait QueryTrait
 
     /**
      * Sets the LIMIT part of the query.
-     * @param int|Expression $limit the limit. Use null or negative value to disable limit.
+     * @param int|Expression|null $limit the limit. Use null or negative value to disable limit.
      * @return $this the query object itself
      */
     public function limit($limit)
@@ -387,7 +387,7 @@ trait QueryTrait
 
     /**
      * Sets the OFFSET part of the query.
-     * @param int|Expression $offset the offset. Use null or negative value to disable offset.
+     * @param int|Expression|null $offset the offset. Use null or negative value to disable offset.
      * @return $this the query object itself
      */
     public function offset($offset)