Hotfix/media kit page issues

[adekbadek]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Fixes a regression introduced in #894, and adjusts Tabs component styling.

How to test the changes in this Pull Request:

1. On release, observe that in the post editor, after focusing on the empty block, the block appender disappears
2. Switch to this branch, observe the block appender is not disappearing
3. Visit or create the media kit page, observe the tabs are working as expected in the editor and in the front-end

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

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[matticbot]

🎉 This PR is included in version 3.2.1 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀