Run tests against WordPress 6.4

[n7studios]

Summary

Run tests against WordPress 6.4, released November 7th.

• Enables WP_DEBUG for PHP 8.1; 8.2 still returns some deprecated notices due to Gravity Forms, outside of our control.
• Removes some unnecessary steps from the GitHub actions.
• Updates the WordPress SQL dump file.

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)