prepare wp 7.1 release

[masteradhoc]

• This will be on-hold until WordPress 7.1 is released!

What?

Drops support for PHP 7.2 and 7.3, raises the minimum PHP version to 7.4 and the minimum WordPress version to 7.0.

Fixes #751

Why?

Per the plugin's version support policy with the release of WordPress 7.1 we'll be dropping the support for WP 6.9.
With WordPress 7.0 and 7.1 be the only supported versions we can enforce PHP 7.4 as its minimum php version.

How?

• Updated Requires PHP header in two-factor.php and readme.txt from 7.2 to 7.4
• Updated Requires at least header in two-factor.php and readme.txt from 6.9 to 7.0
• Updated Tested up to in readme.txt to 7.1
• Updated phpcs.xml.dist: testVersion from 7.2- to 7.4-
• Removed PHP 7.2 and 7.3 from the CI test matrix in .github/workflows/test.yml, removed the four now-redundant exclude entries, and updated the tested WP version from 6.9 to 7.0
• Updated AGENTS.md to reflect the new minimum PHP version

Use of AI Tools

AI assistance: Yes
Tool(s): GitHub Copilot
Model(s): Claude Sonnet 4.6
Used for: Generating the changes across configuration files; all changes were reviewed and verified by me.

Screenshots or screencast

N/A — no UI changes.

Changelog Entry

Development Update - Drop PHP 7.2 and 7.3 support; raise minimum PHP version to 7.4 and minimum WordPress version to 7.0.