Fixes an issue with stats cards breaking out of the container

[cameronterry]

Description of the Change

Fixes an issue introduced by WordPress 6.0 and above on the columns block within the .pmk-stats group block, where the columns/column blocks were breaking out of the container.

Sadly this involved using !important; there might be a better alternative ...

It seems was first introduced into Gutenberg between December 2022 and January 2023 (WordPress/gutenberg#37436) and then included in WordPress Core with the 6.0 release (https://core.trac.wordpress.org/ticket/55505). I confirmed this by downgrading my local to 5.9.3 (wp core update --version=5.9.3 --force) and the fix in this PR wasn't needed. Upgrading to 6.0, the columns broke and the fix was required.

Closes #135

How to test the Change

1. Follow plugin installation steps: https://wordpress.org/plugins/publisher-media-kit/#installation.
2. Publish the "Media Kit" page.
3. Download and activate the Newspack Base theme.
4. Visit the "Media Kit" page, ensure the Cards under "Audience Profiles" is partly stacked (3 on top, 2 beneath) as per the screenshot in the README.md file.
5. Repeat checks for tablet and smartphones, ensuring the display is appropriate for the screensize (i.e. the Cards should be stacked in rows, 1 per card, etc.).

Changelog Entry

Fixed - issue with statistics cards breaking out of container in WordPress 6.0 and above.

Added - New feature
Changed - Existing functionality
Deprecated - Soon-to-be removed feature
Removed - Feature
Fixed - Bug fix
Security - Vulnerability

Credits

Props @cameronterry

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly. (N/A)
• I have added tests to cover my change. (N/A)
• All new and existing tests pass.