Test the PR previewer – update the twentytwentyfour theme

[adamziel]

⚠️ Do not merge! ⚠️

This PR exists to test the user experience of previewing WordPress Pull Requests.

Expected results

Stage of the initial build:

Before it's ready	After it's ready

See #5737

Trac ticket: https://core.trac.wordpress.org/ticket/59416

[github-actions]

Test using WordPress Playground

The changes in this pull request can previewed and tested using a WordPress Playground instance.

WordPress Playground is an experimental project that creates a full WordPress instance entirely within the browser.

Some things to be aware of

• The Plugin and Theme Directories cannot be accessed within Playground.
• All changes will be lost when closing a tab with a Playground instance.
• All changes will be lost when refreshing the page.
• A fresh instance is created each time the link below is clicked.
• Every time this pull request is updated, a new ZIP file containing all changes is created. If changes are not reflected in the Playground instance,
  it's possible that the most recent build failed, or has not completed. Check the list of workflow runs to be sure.

For more details about these limitations and more, check out the Limitations page in the WordPress Playground documentation.

Test this pull request with WordPress Playground.

[adamziel]

Let's keep this PR open until 20.12 as a live demo of the previewer. In the meantime, other PRs will get created and rebased, providing many more examples.