Fix deprecation notice on the question edit screen on PHP 8.1

[m1r0]

Part of https://github.com/Automattic/sensei/issues/7634

Proposed Changes

• Fix the deprecation notice on the question edit screen on PHP 8.1.

Testing Instructions

1. Use PHP 8.1.
2. Add define( 'WP_DEBUG_DISPLAY', true ); in wp-config.php.
3. Go to Sensei LMS -> Questions and select any question.
4. There should be no deprecation notice.
5. The "Quizzes" section should be working as before.

Pre-Merge Checklist

• [x] PR title and description contain sufficient detail and accurately describe the changes
• [ ] Acceptance criteria is met
• [ ] Decisions are publicly documented
• [ ] Adheres to coding standards (PHP, JavaScript, CSS, HTML)
• [ ] All strings are translatable (without concatenation, handles plurals)
• [ ] Follows our naming conventions (P6rkRX-4oA-p2)
• [ ] Hooks (p6rkRX-1uS-p2) and functions are documented
• [ ] New UIs are responsive and use a mobile-first approach
• [ ] New UIs match the designs
• [ ] Different user privileges (admin, teacher, subscriber) are tested as appropriate
• [ ] Legacy courses (course without blocks) are tested
• [ ] Code is tested on the minimum supported PHP and WordPress versions
• [ ] User interface changes have been tested on the latest versions of Chrome, Firefox and Safari
• [ ] "Needs Documentation" label is added if this change requires updates to documentation
• [ ] Known issues are created as new GitHub issues

[github-actions[bot]]

Test the previous changes of this PR with WordPress Playground.

[github-actions[bot]]

Test the previous changes of this PR with WordPress Playground.