Not able to update privileges on User

[kundansable]

Please note that security bugs or issues should be reported to security@pgadmin.org.

Describe the bug

When user wants to edit membership of any other user, if select different options for existing membership from select box and save it. it won't update the user membership. If you see in SQL tab, it only show revoke option for user, instead of granting new privilege and removing previous one.

To Reproduce

Steps to reproduce the behavior:

1. Go to 'Login/Group Roles'
2. Right Click on any existing user and open properties
3. Go to Membership tab on modal. check if there is any privilege selected in Members of or Members section.
4. Select different privilege than existing in same select box.
5. check SQL tab in modal,
6. Save the data.
7. Reopen the properties for same user, it won't reflect the privilege that you have selected.

Expected behavior
Privilege should get updated, even if we update on existing privilege select box. currently we have to remove current privilege to add new privilege.

Screenshots

Additional context

Add any other context about the problem here.