Prevents the removal of all user groups from a user (#19995)

* Prevents the removal of all user groups from a user.

* Add additional user group when removing

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Co-authored-by: mole <nikolajlauridsen@protonmail.ch>

tests/Umbraco.Tests.AcceptanceTest/tests/DefaultConfig/Users/User.spec.ts

@@ -642,4 +642,4 @@ test.skip('cannot remove all user group from a user', {tag: '@release'}, async (
 
   // Assert
   await umbracoUi.user.isErrorNotificationVisible();
-});
+});