Bump PHP version requirement from 5.2.3 to 7.2.25

Summary:
Supporting PHP 8.4 requires syntax introduced in PHP 7.1.
Thus require PHP version 7.2.25 released on 21 November 2019.
Phorge previously required version 5.2.3 released on 31 May 2007.

Closes T15047

Test Plan: None.

Reviewers: O1 Blessed Committers, Sten, avivey

Reviewed By: O1 Blessed Committers, Sten, avivey

Subscribers: Sten, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15047

Differential Revision: https://we.phorge.it/D25815