Fix: Ensure Carousel thumbnails are now responsive.

[badasswp]

Description

This PR addresses the following ticket: #2605. It adds the missing class to enable Carousel thumbnails become responsive.

Screenshots

Types of changes

Bug fix (non-breaking change which fixes an issue)

How has this been tested?

• Insert Gallery Carousel block.
• Observe that images are now responsive.
• Tested with different browsers and themes to ensure consistency.

Acceptance criteria

Images should now have class with value wp-image-{id}

Checklist:

• [x] My code is tested
• [x] My code follows accessibility standards
• [ ] My code has proper inline documentation
• [ ] I've included any necessary tests
• [ ] I've included developer documentation
• [ ] I've added proper labels to this pull request