REST API: Grant super admin to site health test user.

The current user needs to be a super admin to access Site Health on multisite.

Follow up to [49154].
See #48105.


git-svn-id: https://develop.svn.wordpress.org/trunk@49155 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/rest-api/rest-site-health-controller.php

@@ -50,6 +50,10 @@ class WP_Test_REST_Site_Health_Controller extends WP_Test_REST_TestCase {
 				'role' => 'administrator',
 			)
 		);
+
+		if ( is_multisite() ) {
+			grant_super_admin( self::$admin );
+		}
 	}
 
 	/**