Documentation: Update PHPCompatibilityWP version recommendation to 7.2

[johnjago]

As of WordPress 6.6, released on 16 July 2024, WordPress no longer supports PHP 7.0 and 7.1, so I’ve updated the recommended testVersion for PHPCompatibilityWP to be 7.2 in the README.

References:

• https://make.wordpress.org/core/2024/04/08/dropping-support-for-php-7-1/
• https://wordpress.org/news/2024/07/dorsey/ (6.6 released)

[jrfnl]

I'm in two minds about this change. For plugins/themes, WPCS, by default, presumes support for the last three versions of WP Core and two of those do not have a minimum supported version of PHP 7.2 yet.

At the same time, the phrasing in the README says "the same PHP versions as WordPress Core supports", so leaving that recommendation at PHP 7.0 is not correct either.

Also note that any update like this should probably also update the phpcs.xml.dist.sample file.

[jrfnl]

I believe it is time to merge this by now.

Note: I will submit a separate PR to make some updates to the phpcs.xml.dist.sample ruleset. That doesn't need to block this PR.

[jrfnl]

I've taken the liberty to merge in the dev branch to get this into a mergable state. I will (squash)-merge this once the build has passed.