Resolves https://github.com/Automattic/sensei-security/issues/21.

Proposed Changes

Switch to using wp_json_encode instead of json_encode when searching courses on the Module admin page.

Testing Instructions

1. Browse to Sensei LMS > Modules.
2. Search for a course in the Course(s) dropdown and ensure it works.

Pre-Merge Checklist

• PR title and description contain sufficient detail and accurately describe the changes
• 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
• Code is tested on the minimum supported PHP and WordPress versions