Build/Test Tools: Automatically skip tests in the ms-required and ms-excluded groups.

This removes the need to manually call `$this->skipWithMultisite()` and `$this->skipWithoutMultisite()` from within the test when the test only runs without Multisite or only runs on Multisite, respectively.

Props jdgrimes for the suggestion.

Fixes #40531


git-svn-id: https://develop.svn.wordpress.org/trunk@40564 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/user.php

@@ -652,8 +652,6 @@ class Tests_User extends WP_UnitTestCase {
 	 * @group ms-required
 	 */
 	function test_illegal_user_logins_multisite() {
-		$this->skipWithoutMultisite();
-
 		$user_data = array(
 			'user_login' => 'testuser',
 			'user_email' => 'testuser@example.com',