Bundled Themes: Make Twenty Twenty the new default theme.

After being imported in [46271], Twenty Twenty can now be set as the default theme in WordPress.

See #48110.
Props desrosj, ocean90.

git-svn-id: https://develop.svn.wordpress.org/trunk@46278 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/theme.php

@@ -18,6 +18,7 @@ class Tests_Theme extends WP_UnitTestCase {
 		'twentysixteen',
 		'twentyseventeen',
 		'twentynineteen',
+		'twentytwenty',
 	);
 
 	function setUp() {