Fix the 'test_remove_invalid_element_pseudo_selectors' test case (WordPress#47049)

Author: Mamaduka

phpunit/class-wp-theme-json-test.php

@@ -894,6 +894,11 @@ public function test_remove_invalid_element_pseudo_selectors() {
 									'background' => 'blue',
 								),
 							),
+							':seen'  => array(
+								'color' => array(
+									'background' => 'ivory',
+								),
+							),
 						),
 					),
 				),