Update 2023-03-17-new-in-php-83.md

[PtrTn]

Fix return type in example, which would throw fatal

This applies the same fix to the new in php 8.3 post as https://github.com/brendt/stitcher.io/commit/fe5e48a69a60534583056f2ac007c9522e3b631d does to the override in php 8.3 post

[brendt]

Thanks!