Fix return type

Author: VincentLanglet

date/date_c.php

@@ -490,7 +490,7 @@ public function __wakeup(): void {}
 
     /**
      * @param DateTimeInterface $object
-     * @return DateTimeImmutable
+     * @return static
      * @since 8.0
      */
     public static function createFromInterface(DateTimeInterface $object): DateTimeImmutable {}
@@ -881,7 +881,7 @@ public static function __set_state($array) {}
 
     /**
      * @param DateTimeInterface $object
-     * @return DateTime
+     * @return static
      * @since 8.0
      */
     public static function createFromInterface(DateTimeInterface $object): DateTime {}