Bundled Themes: Make Twenty Twenty-One the default theme.

After being imported in [49216], Twenty Twenty-One can now be set as the default theme in WordPress.

See #48110.

git-svn-id: https://develop.svn.wordpress.org/trunk@49220 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-theme.php

@@ -59,6 +59,7 @@ final class WP_Theme implements ArrayAccess {
 		'twentyseventeen' => 'Twenty Seventeen',
 		'twentynineteen'  => 'Twenty Nineteen',
 		'twentytwenty'    => 'Twenty Twenty',
+		'twentytwentyone' => 'Twenty Twenty-One',
 	);
 
 	/**