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/countUsers.php

@@ -12,8 +12,6 @@ class Tests_User_CountUsers extends WP_UnitTestCase {
 	 * @group ms-excluded
 	 */
 	public function test_count_users_is_accurate( $strategy ) {
-		$this->skipWithMultisite();
-
 		// Setup users
 		$admin = self::factory()->user->create( array(
 			'role' => 'administrator',
@@ -60,8 +58,6 @@ class Tests_User_CountUsers extends WP_UnitTestCase {
 	 * @dataProvider data_count_users_strategies
 	 */
 	public function test_count_users_multisite_is_accurate( $strategy ) {
-		$this->skipWithoutMultisite();
-
 		// Setup users
 		$admin = self::factory()->user->create( array(
 			'role' => 'administrator',