Mk/bsd.default-versions.mk: Change PHP default version to 8.1

Switching php DEFAULT_VERSION from 8.0 to 8.1. php 8.0 Active support
ends on 2022-11-26. This will not be merged in quarterly.

PR: 266854
Tested by: antoine
Approved by: ale
Relnotes: https://www.php.net/supported-versions.php
Sponsored by: Bounce Experts