Tests: Add test against PHP 8.5

[masteradhoc]

Describe the bug

Support for PHP 8.5 has been added in WordPress Release of 6.9.
We should add a test for 8.5 as well.

Steps to Reproduce

1. go to a PR that has the tests already passed
2. see the tests only go up to php 8.4

Screenshots, screen recording, code snippet

No response

Environment information

No response

Please confirm that you have searched existing issues in this repository.

Yes

Please confirm that you have tested with all plugins deactivated except Two-Factor.

Yes