Add missing throw tag

Author: VincentLanglet

date/date_c.php

@@ -245,6 +245,7 @@ public static function getLastErrors(): array|false {}
      * @param string $modifier <p>A date/time string. Valid formats are explained in
      * {@link https://secure.php.net/manual/en/datetime.formats.php Date and Time Formats}.</p>
      * @return static|false Returns the newly created object or false on failure.
+     * @throws DateMalformedStringException
      * Returns the {@link https://secure.php.net/manual/en/class.datetimeimmutable.php DateTimeImmutable} object for method chaining or <b>FALSE</b> on failure.
      */
     #[Pure]