Tests: Fix _load_textdomain_just_in_time PHP Notice

[n7studios]

Summary

WordPress 6.7 displays a PHP notice if a Theme or Plugin calls load_plugin_textdomain too early i.e. before the WordPress init hook and WP_DEBUG is enabled.

This Plugin's tests run with WP_DEBUG enabled, and due to activating third party Plugins to run specific tests against, we get errors:

This PR resolves by suppressing the _load_textdomain_just_in_time PHP notice in our automated testing via use of a Plugin, whilst allowing other notices to still display and be detected.

Also fixes cron tests failing due to a change in the admin UI URL in WP Crontrol 1.17.1, released November 23rd.

Testing

Existing tests pass.

Checklist

• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• Security and Sanitization requirements have been followed
• I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)

[noelherrick]

Would this still catch errors in the Kit plugin if it made this mistake?

[n7studios]

Would this still catch errors in the Kit plugin if it made this mistake?

It only suppresses the _load_textdomain_just_in_time error, caused by third party Plugins calling load_plugin_textdomain too early:
https://stackoverflow.com/questions/79198701/notice-function-load-textdomain-just-in-time-was-called-incorrectly

We load our language files correctly by using the init hook, so the Kit plugin won't be triggering this:
https://github.com/Kit/convertkit-wordpress/blob/main/includes/class-wp-convertkit.php#L51