Build/Test Tools: Introduce ms-required and ms-excluded groups for tests.

Tests in the `ms-excluded` group are now excluded when running tests with multisite enabled, and tests in the `ms-required` group are excluded when running tests without multisite enabled. The end result is a significantly reduced number of skipped tests polluting PHPUnit's output, which means verbose mode can be used to more easily see which tests are skipped or incomplete, and why.

See #40531


git-svn-id: https://develop.svn.wordpress.org/trunk@40520 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/user/countUsers.php

@@ -9,6 +9,7 @@ class Tests_User_CountUsers extends WP_UnitTestCase {
 	 * @ticket 22993
 	 *
 	 * @dataProvider data_count_users_strategies
+	 * @group ms-excluded
 	 */
 	public function test_count_users_is_accurate( $strategy ) {
 
@@ -57,6 +58,7 @@ class Tests_User_CountUsers extends WP_UnitTestCase {
 	/**
 	 * @ticket 22993
 	 * @group multisite
+	 * @group ms-required
 	 *
 	 * @dataProvider data_count_users_strategies
 	 */