Fix deprecated usort return type

[thunderdw]

Description

Returning a boolean from a usort callback has been deprecated since PHP 8.0. This PR updates a callback to fix the deprecation error.

Related Issue:

Types of changes

This PR updates a usort callback to use the spaceship operator instead of a standard < comparison.

Screenshots

This has been tested in the following browsers

Tested in Chrome; the change shouldn't have any browser-specific behavior.

• [x] Chrome
• [ ] Firefox
• [ ] Edge
• [ ] Safari

Merge Checklist

• [ ] This PR passes all automated checks (will appear once pull request is submitted)
• [x] My code has been tested in the latest version of WordPress.
• [x] My code does not have any warnings from ESLint.
• [x] My code does not have any warnings from StyleLint.
• [x] My code does not have any warnings from PHPCS.
• [x] My code follows the WordPress coding standards.
• [x] My code follows the accessibility standards.
• [x] All new functions and classes have code documentation.

[danieliser]

We will be officially changing min PHP version of the plugin to 7.4 in the next few versions, can't merge this change til then unfortunately as <=> is PHP 7+.

We could refactor it long form though with more conditionals.