XWIKI-22286: Add automated test for "Show User and Group Rights"

* Fix test

(cherry picked from commit ed0a7fc)

Author: vmassol

xwiki-platform-core/xwiki-platform-administration/xwiki-platform-administration-test/xwiki-platform-administration-test-docker/src/test/it/org/xwiki/administration/test/ui/UsersGroupsRightsManagementIT.java

@@ -740,6 +740,11 @@ void rightsShowUsersAndGroups(TestUtils setup, TestReference testReference)
 
         // Create the admin user so that we can verify it's listed in the Rights table.
         setup.createAdminUser();
+        // createAdminUser() logs in as the non-superadmin "Admin" user; log back in as superadmin so that
+        // navigating to the (global and page) administration is race-free, matching the rest of this class. The
+        // "Admin" user document is created via REST regardless of who is logged in, so it's still listed in the
+        // Rights table below.
+        setup.loginAsSuperAdmin();
 
         // Global level -> Administer Wiki -> Users & Rights -> Rights.
         AdministrationPage administrationPage = AdministrationPage.gotoPage();