Tests: Dont test against WP 6.7 anymore

[masteradhoc]

Describe the bug

Currently we're testing all PRs against WP 6.7, latest stable (WP 6.9) and WP 7.0 trunk.
We should upgrade the tests against WP 6.7 to WP 6.8.

Steps to Reproduce

1. go to a PR that has the tests already passed
2. see the tests are running against WP 6.7 instead a supported version

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

[jeffpaul]

@masteradhoc please ensure you also update the following to 6.8 then:

two-factor/two-factor.php

Line 14 in 8b998d4

* Requires at least: 6.7