Bump PHP and Python versions on FreeBSD

Summary:

• Python 3.7 -> Python 3.8
• PHP 7.4 -> PHP 8.1

The move to PHP 8.1 allows to support enums and a|b union types in parameters.

This is required for Zed development for the geo library.

Test Plan: Test on WindRiver

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2476